reverse order of operands
improve logic
Refactor include_columns and exclude_columns
remove n_data_cols
Make more use of colnames property
correct inverse and start a new Travis build.
added a new "Antenna Gain" equivalency (Jy to K)
fixed equivalency call
add to __all__
fixed tests & examples as per @mdboom's comment
fixed docstring tests: reduce # of significant digits
same as previous commit, but for the <Quantity object.  Unfortunately,
this hides the units...
added some more clarification & references to the jytok equiv
fixed doctest
name change: jytok -> brightness_temperature
doc formatting change
added eqiv to changes
doc update (tb equiv)
documentation fixes in tb equivalency
doc fix attempt cont'd; intersphinx not working for quantity though