Basic start to array implementation of dictionary.

Really, at the moment, this is a vector implementation. I'd like
to use actual dynamically-allocated arrays instead, just for fun.

Also includes a basic test of functionality, which works, in the
unittests/ directory, as well as a very simplistic Makefile for that test.
Merge remote-tracking branch 'origin/devel' into devel

There didn't seem to be anything different between them, but git
said they needed to be merged. Not sure what happened...
Changed the name of array_dict to ArrayDict.

This is more consistent with the rest of my naming style,
and indicates ArrayDist is a user-defined type.