Most of Brian Hears works

Still missing:
- FilterbankGroup
- Sound slicing (may not be possible)
Slicing sounds alternative
Majority of Brian 1 Hears works
Update travis config to install brian (for brian 1 hears bridge)
Documentation for Brian 1 Hears bridge
Properties work with Brian 1 hears bridge now
Don't install brian1 for testing; add Python 3.4 to the testing matrix
Mock brian1 when generating the documentation
Fix/add links in the brian hears bridge docs
explicitly ignore the brian2.hears file for testing, otherwise the doctest search will import it, failing on Python 3
Fix parsing/rendering for Python 3.4 (new ast.NameConstant)
Merge pull request #268 from brian-team/brian1hears_bridge

Brian 1 Hears bridge