New tag-formats variable and ported index_format coloring, nested conditionals, and date conditional patches

Changes made:

1. New 'tag-formats' conditional used to assign index_format sequences to individual tags. This allows placing a transformed tag name in a specific spot on the index line. Format used is %Gx where 'x' is configurable. This it an alternative to %g that simply lists all tags in a non-deterministic fashion.

2. Ported the nested if-else conditional patch. This is awesome when used with tag-formats and date conditionals.

3. Ported the date conditional patch. This allows fuzzy date formats (i.e. today, yesterday, MM/DD, YY:MM:DD, etc).

4. Ported the index coloring patch. This allows individual items on the index line to be a different color (i.e. date, author, subject, tags, etc). See new coloring formats in manual.txt.

5. New index_tags and index_tag color highlights. index_tags specifies color for %g and index_tag takes a tag name argument to color with %Gx.

New hotness:

![2013-10-23-161225_1908x1046_scrot](https://f.cloud.github.com/assets/515747/1395318/2f67d0ac-3c39-11e3-9296-37a1d12e26db.png)