GSOC: Unify the commands `git tag -l`, `git brach -l` and `git for-each-ref`

Hello All,

As part of GSoC I'm working on the Unification of 'for-each-ref', 'tag -l' and 'branch -l'.

Current Progress:

1. Building ref-filter.{c,h} from for-each-ref.
This is the process of creating an initial library for the unification
by moving most of the code from for-each-ref to ref-filter.{c,h}.
Merged into next

2. Add options to ref-filter.
This includes the porting of --points-at, --contains, --merged,
--no-merged options from builtin/branch.c and builtin/tag.c, Also the
implementation of these options into for-each-ref.
Merged to next

3. Port builtin/tag.c to use ref-filter.
Here we port tag.c to use ref-filter and also port the --format,
--sort and --merged and --no-merged options to builtin/tag.c.
Version 13 can be found here:
* http://thread.gmane.org/gmane.comp.version-control.git/276363
There was a lot of discussion on v12 (especially how %(align)...%(end) should be
handling '--quote') which can be found here:
* http://thread.gmane.org/gmane.comp.version-control.git/276133

4. Port builtin/branch.c to use ref-filter filtering APIs.
Here we make use of the filtering APIs provided by ref-filter to filter out
branches. Also make it learn the '--points-at' command.
version 3 can be found here:
* http://thread.gmane.org/gmane.comp.version-control.git/276377

As my mentors suggested, I'm working on the printing aspects of branch.c now. This involves supporting %(if)....%(then)....%(else)....%(end). and making branch.c use show_ref_array_item() rather than using its own implementation.

As the ground has been laid for %(align)....%(end) atom, the work shouldn't be of much difficulty.

Will push most of my work to github: github.com/KarthikNayak/git