Thanks to @MinchinWeb for noticing.

The Dot output now uses these colors for the nodes.

Conflicts:
	topydo/lib/ListFormat.py

The humanize_date function was therefore moved out ListFormat.py towards
Utils.py.

It has full name now, a priority and a due date. The legend is no longer
printed.

Don't just consider the first p tag value in a todo item, consider all
of them.

Given these dependencies:

A id:1
B p:1
C p:1 id:2
D p:1 p:2

A -> B
A -> C
A -> D
C -> D

The relation A -> D is superfluous (A -> C, C -> D). However, the p:1
tag in D would not be removed, because relation 1 still exists (A -> B).

Therefore a new function is added that identifies p: tags which have no
corresponding edge in the internal dependency graph (rather than looking
at the value of the edge).

By doing so, the parent items, which are hidden by default, are shown in
the dependency graph. Otherwise it would only print child items which is
not so useful.

Conflicts:
	setup.py
	topydo/lib/PrettyPrinterFilter.py

This assertion was missing in commit 6bb804dc.

To complete a todo item that you finished yesterday, run

    topydo do -d yesterday

Or

    topydo do -d -1d

Inspired by issue #82.

Prefix all node names with an underscore, print the proper number
through the "label" attribute.

When an ordinal tag filter is negated (i.e. -id:1), then this isn't seen
as a negation but as an ordinal tag filter with tag -id and value 1.
Which isn't likely to exist, resulting in every todo item to be excluded
from the result.

Related to commit cde8f8ed

https://bitbucket.org/ned/coveragepy/issues/90/lambda-expression-confuses-branch

Fix priority colors when using colorblocks.

Removed `topydo.lib.Colors.Colors.get_priority_colors()` and added in
its place `topydo.lib.Colors.Colors.get_priority_color(p_priority)`.

Also moved `_name_to_ansi`, `_name_to_int`, and `_get_ansi` outside of
the class.

Conflicts:
	setup.py
	topydo/lib/PrettyPrinterFilter.py