Integrate sphinx, travis, tox, py.test and rtd

- [x] Create a sphinx doc folder
- [x] Set up RTD hooks
- [x] Sphinx extensions: numpydoc, ipython
- [x] Fix [conf.py](doc/source/conf.py) to make it work with RTD
- [x] Refactor class names in [reactive.py](translucent/reactive.py)
- [x] Set up Travis CI hooks, fix requirements
- [x] Make sure stuff builds on Travis at least for py27
- [x] Remove pandas hard dependency
- [x] Try to make tests run on Travis py26
- [x] Integrate Tox
- [x] Integrate coveralls.io
- [x] Switch to py.test, remove nose dependency
- [x] Integrate Travis with Tox, build coverage only once
- [x] Repair coverage on Tox
- [x] Rename `cache` to `memoize`
- [x] Initial basic API reference for (translucent/reactive.py)