Add some docstrings

download.py is still a little light on docstrings.
Initial work on some documentation
Documentation bugfixes
TODO: implementation details of interpolation
Fix typo
Merge pull request #33 from danielrichman/docs

Some documentation (intro, setup, overview, core predictor basics); TODO: interpolation guts.
put things in conf.py so rtd can build docs ok
Merge pull request #35 from adamgreig/fixdocs

put things in conf.py so rtd can build docs ok
Documentation: Interpolation, wind data overview, misc fixes
Replace Forwards Euler with RK4
Fix typo, add to copyright
Fix typo Datset -> Dataset
Merge pull request #37 from danielrichman/rk4

Replace Forwards Euler with RK4
Merge pull request #38 from danielrichman/more-docs

Documentation: Interpolation, wind data overview, misc fixes
Binary Search for the point where the termination condition becomes true
Replace closures with cdef'd class methods
Merge remote-tracking branch 'daniel/cython-noclosures'