Add comments to the SCSS Lint config file [ci skip]

Also add some previously missing linters.

.scss-lint.yml

@@ -7,21 +7,44 @@ exclude:
   - 'app/assets/stylesheets/pages/emojis.scss'
 
 linters:
+  # Reports when you use improper spacing around ! (the "bang") in !default,
+  # !global, !important, and !optional flags.
   BangFormat:
     enabled: false
   
+  # Whether or not to prefer `border: 0` over `border: none`.
   BorderZero:
     enabled: false
   
+  # Reports when you define a rule set using a selector with chained classes
+  # (a.k.a. adjoining classes).
+  ChainedClasses:
+    enabled: false
+
+  # Prefer hexadecimal color codes over color keywords.
+  # (e.g. `color: green` is a color keyword)
   ColorKeyword:
     enabled: false
   
+  # Prefer color literals (keywords or hexadecimal codes) to be used only in
+  # variable declarations. They should be referred to via variables everywhere
+  # else.
   ColorVariable:
     enabled: false
   
+  # Which form of comments to prefer in CSS.
   Comment:
     enabled: false
+
+  # Reports @debug statements (which you probably left behind accidentally).
+  DebugStatement:
+    enabled: false
   
+  # Rule sets should be ordered as follows:
+  # - @extend declarations
+  # - @include declarations without inner @content
+  # - properties, @include declarations with inner @content
+  # - nested rule sets.
   DeclarationOrder:
     enabled: false
 
@@ -32,15 +55,25 @@ linters:
   DisableLinterReason:
     enabled: true
   
+  # Reports when you define the same property twice in a single rule set.
   DuplicateProperty:
     enabled: false
   
+  # Separate rule, function, and mixin declarations with empty lines.
   EmptyLineBetweenBlocks:
     enabled: false
   
+  # Reports when you have an empty rule set.
   EmptyRule:
     enabled: false
   
+  # Reports when you have an @extend directive.
+  ExtendDirective:
+    enabled: false
+
+  # Files should always have a final newline. This results in better diffs
+  # when adding lines to the file, since SCM systems such as git won't
+  # think that you touched the last line.
   FinalNewline:
     enabled: false
   
@@ -53,12 +86,17 @@ linters:
   HexNotation:
     enabled: true
   
+  # Avoid using ID selectors.
   IdSelector:
     enabled: false
   
+  # The basenames of @imported SCSS partials should not begin with an
+  # underscore and should not include the filename extension.
   ImportPath:
     enabled: false
   
+  # Avoid using !important in properties. It is usually indicative of a
+  # misunderstanding of CSS specificity and can lead to brittle code.
   ImportantRule:
     enabled: false
   
@@ -67,33 +105,51 @@ linters:
     enabled: true
     width: 2
   
+  # Don't write leading zeros for numeric values with a decimal point.
   LeadingZero:
     enabled: false
   
+  # Reports when you define the same selector twice in a single sheet.
   MergeableSelector:
     enabled: false
   
+  # Functions, mixins, variables, and placeholders should be declared
+  # with all lowercase letters and hyphens instead of underscores.
   NameFormat:
     enabled: false
   
+  # Avoid nesting selectors too deeply.
   NestingDepth:
     enabled: false
 
+  # Always use placeholder selectors in @extend.
   PlaceholderInExtend:
     enabled: false
 
+  # Sort properties in a strict order.
   PropertySortOrder:
     enabled: false
   
+  # Reports when you use an unknown or disabled CSS property
+  # (ignoring vendor-prefixed properties).
   PropertySpelling:
     enabled: false
   
+  # Configure which units are allowed for property values.
+  PropertyUnits:
+    enabled: false
+
+  # Pseudo-elements, like ::before, and ::first-letter, should be declared
+  # with two colons. Pseudo-classes, like :hover and :first-child, should
+  # be declared with one colon.
   PseudoElement:
     enabled: false
   
+  # Avoid qualifying elements in selectors (also known as "tag-qualifying").
   QualifyingElement:
     enabled: false
   
+  # Don't write selectors with a depth of applicability greater than 3.
   SelectorDepth:
     enabled: false
   
@@ -113,9 +169,12 @@ linters:
     enabled: true
     allow_single_line_rule_sets: true
 
+  # Split selectors onto separate lines after each comma, and have each
+  # individual selector occupy a single line.
   SingleLinePerSelector:
     enabled: false
   
+  # Commas in lists should be followed by a space.
   SpaceAfterComma:
     enabled: false
   
@@ -128,29 +187,75 @@ linters:
   # colon.
   SpaceAfterPropertyName:
     enabled: true
+
+  # Variables should be formatted with a single space separating the colon
+  # from the variable's value.
+  SpaceAfterVariableColon:
+    enabled: false
+
+  # Variables should be formatted with no space between the name and the
+  # colon.
+  SpaceAfterVariableName:
+    enabled: false
   
+  # Operators should be formatted with a single space on both sides of an
+  # infix operator.
   SpaceAroundOperator:
     enabled: false
   
   # Opening braces should be preceded by a single space.
   SpaceBeforeBrace:
     enabled: true
+
+  # Parentheses should not be padded with spaces.
+  SpaceBetweenParens:
+    enabled: false
   
+  # Enforces that string literals should be written with a consistent form
+  # of quotes (single or double).
   StringQuotes:
     enabled: false
 
+  # Property values, @extend, @include, and @import directives, and variable
+  # declarations should always end with a semicolon.
   TrailingSemicolon:
     enabled: false
 
+  # Reports lines containing trailing whitespace.
   TrailingWhitespace:
     enabled: false
 
+  # Don't write trailing zeros for numeric values with a decimal point.
+  TrailingZero:
+    enabled: false
+
+  # Don't use the `all` keyword to specify transition properties.
+  TransitionAll:
+    enabled: false
+
+  # Numeric values should not contain unnecessary fractional portions.
   UnnecessaryMantissa:
     enabled: false
 
+  # Do not use parent selector references (&) when they would otherwise
+  # be unnecessary.
   UnnecessaryParentReference:
     enabled: false
+  
+  # URLs should be valid and not contain protocols or domain names.
+  UrlFormat:
+    enabled: false
+
+  # URLs should always be enclosed within quotes.
+  UrlQuotes:
+    enabled: false
+
+  # Properties, like color and font, are easier to read and maintain
+  # when defined using variables rather than literals.
+  VariableForProperty:
+    enabled: false
 
+  # Avoid vendor prefixes. Or rather: don't write them yourself.
   VendorPrefix:
     enabled: false