markdown: Fix "metadata not closed" bug. More tests.

Domain names must be unique in cert bundle request or really bad things happen (like, um, a panic)

markdown: fix json front matter parse issue when body content is long

We can't use json meta parser's remaining buffered data as the markdown body
because it may not contain the entire original content.
Now we adopt the way like toml and yaml parser's way to extract the meta content
at first.

Also when spilting the meta data and content body, additional io.Copy is
unnecessary.

Fix issue #355
Signed-off-by: Tw <tw19881113@gmail.com>

wrap lines to 80 characters

more copy edits

also linked to bug reporting article.

add links to inspired by projects and updated language with golang.

copy edit to wrap around 80 chars

not all lines wrap at 80 characters but now most do.

rewrite: Use middleware.Replacer for simple rule

proxy: Two small websocket fixes

browse: allow consecutive spaces in the header

Add a few super minor lint fixes

Other lint warnings left behind are ones due to external package and
due to maintainer's preferences.

Made a faulty assumption that virualhosts could share acme proxy handlers; turns out they can't without fumbling up the middleware configuration (middleware chains overlap and cross over into other virtualhosts)!

Hosts which are eligible for automatic HTTPS have default port "https" but other hosts (wildcards, loopback, etc.) have the default port 2015. The default host of empty string should be more IPv6-compatible.

proxy: make http header block scoped

proxy: make tests workable when offline

Instead of accessing the google website, we setup a local server
for test, then tests will work fine even we are offline.

Fix issue #346
Signed-off-by: Tw <tw19881113@gmail.com>

Each proxy block should could specify its own http header
instead of sharing a global one.

Fix issue #341
Signed-off-by: Tw <tw19881113@gmail.com>

proxy: 'except' property to ignore subpaths