Improve BSD licensed text processing tools

[Jesse Hagewood]

Here are some of the things I accomplished during this week:

- Implemented skeleton functions and set up .ti for adding functionality as
an mdoc macro in mdocml.
- Corrected some style errors I overlooked in diff3 that Dag-Erling pointed
out for me.
- Completed GNU compatibility for the diff options --unified and --context.
- Implemented --normal in diff.
- Started working on implementing the diff options --ignore-tab-expansion
and --line-format.

According the the schedule I have set up for SoC, today I move to diff as a
primary focus. Because I've been studying and working with diff's source
about a week in advance, I've come up with a list of to-do's for the next
few weeks:

https://socsvn.freebsd.org/socsvn/soc2012/jhagewood/diff/TODO

This following week, I will complete --ignore-tab-expansion, --line-format,
--ignore-blank-lines, and begin working on better support for large files
in diff.

As for mdocml, I still plan to work on the implementing the macros I have
already started working on as a secondary focus during the summer. I will
probably spend a few hours during the weekends trying to complete what I
started while I work on the diff utilities during the week.

My project wiki:
http://wiki.freebsd.org/SummerOfCode2012/JesseHagewood

SVN repo:
https://socsvn.freebsd.org/socsvn/soc2012/jhagewood/

- Jesse Hagewood