Bug#812979: Please add python bindings package

[Emmanuel Bourg]

Hi Thomas,

I think it would be preferable for every language to package the runtime
part of antlr separately. This will make the main antlr package easier
to maintain, and each runtime can be maintained by a language specific
team mastering the subtleties of its environment.

This is for the runtime only, the generator part for the other languages
remains in the main antlr3 package obviously.

Emmanuel Bourg