palette: Type conversion bug
tco: Adding .decorate method

Now you can do

    "{{red:grey:b London}} Underground".decorate

to highlight just parts of a string.
palette: Don't use ANSI when not configured

The matching results were extremely inaccurate when the ANSI colour
palette were not configured properly. This patch disables matching
against them uless they are set up.

Fixes #4
palette: Minor comments rewording