Moved alfa to alfalfa, cleaned up alfalfa/core.py (separated cross-identification and spectra download routines), small docstring change in sdss/core.py, and added alfalfa.rst to docs.
Added a line about retrieving the entire ALFALFA catalog in alfalfa.rst.
Forgot to rename test_alfa.py to test_alfalfa.py.
Merge pull request #107 from mirochaj/master

ALFALFA restructuring/bug-fix/docs.