Integration of astropy.units in sunpy codebase

Attempt to integrate the astropy.units into sunpy. Every function that were taking or giving a quantity now must have astropy quantity associated with them. Please tell me if I have made mistakes anywhere, or if it could be done in better way, I will make changes! 
Thank you!   
Ping @ehsteve 

everywhere I looked I found a different equation for this (e.g.,  http://www.meteorobs.org/maillist/msg09197.html ) do we have the sources of the one we use?