naive Sphinx documentation

- translated all docstrings from Markdown to ReST
- added trivial documentation configuration
fix ReST conversion error
converted docstrings to numpy style ReST format

- all parameters are documented
- all return values are documented
- every function and method has an example
added documentation for class members
removed incorrect information from README

we still have to add more information though
a few small changes suggested by mgeier
Move module docstring to the top of the file
Move documentation to doc/ subdirectory
Remove superfluous toctree directive
Change to automodule and use source order
Move property documentation from __init__() to the properties
Change display of return type
Shorter summary of endian-ness
Remove names of return values from docs
Kill open()
Re-order functions

See #57.
Re-order methods within SoundFile

See #57.
Use the __init__() docstring as class documentation
Add requirements file for Sphinx
Add mock modules to avoid full installation for Sphinx