Added diff_rot function.
TESTS!
Tidy
Change to timedelta object
Howard Reference
more Reference
Finished modifications and added Snodgrass paramters
Author modification
Merge branch 'diff_rot' of https://github.com/Cadair/sunpy into diff_rot

Conflicts:
	sunpy/coords/util.py
Merge pull request #401 from Cadair/diff_rot

Tided version of previously submitted diff_rot code
Fix for lightcurve tests on build server
Merge pull request #413 from nabobalis/staging

Fix for lightcurve tests on build server
Travis Fight - Round 1
Merge branch 'staging' of https://github.com/sunpy/sunpy into staging
Travis Fight - Round 2
Travis Fight - Round 3 - SciPy
Travis Fight - Round 4 - SciPy
Travis Fight - Round 5 - suds
Travis Fight 6
Travis Fight 7 - RAKES