New plugin system and docs.

[Dave Camp <dave ximian com>]

I checked in the new plugin system.  Take a look.

I also wrote a little bit of documentation for people getting started
hacking anjuta2.  You can read it at

http://primates.ximian.com/~dave/misc/hacking-anjuta2.html

The source for the document is in anjuta2/docs/hacking.xml.

Have fun,
-dave