Profiles

Made a pull request while I work on this in case you have comments.
Remove the `invert` option.
Instead leave this step up to the user before calling this functions.

Use the Astropy mask convention stated [here](http://astropy.readthedocs.org/en/latest/nddata/index.html#getting-started):
> A mask value of True indicates a value that should be ignored, while a mask value of False indicates a valid value.