Keep stable and dev versions of documentation

[tbekolay]

We make available a stable and dev version of Nengo on http://nengo.ca/download. We should also provide matching version of the documentation.

[codemercenary]

This problem is solvable with Maven. Anything artifacts put in Central will also require documentation jars be attached. Putting the documentation online becomes a matter of adding one more step to an already-explicit release process.

[tbekolay]

Great, sounds good! I'm still merging in the Maven commits -- the main problem is that not all of the Ant functionality is reimplemented in Maven, so we can't do a proper release yet, but I'm just rewriting them now using Maven's AntRun plugin.

[codemercenary]

If you like you can branch my pull request into something else on your repo, and we can work together on this.

[tbekolay]

Right, yeah. I'll merge it into the existing maven repository.