Added brief description to set_source_peakabsmag() in models.py and added an example in models.rst
PEP8'd models.py. Added parameters to set_source_peakabsmag()
Fixed trailing white space in models.py
Update models.rst

Fix typo in model docs
Merge pull request #40 from sofiatti/master

Added set_source_peakabsmag() to documentation and added method description
document math of SALT2 model covariance in docstring
add write_griddata_ascii for testing
add description of SALT2.bandflux_rcov and test
add weightedcov function & test