Fix some doc errors in fits.py.  Also add new writeFile function to write an hdu_list.
(#417)
Fix wrong 'if hdu_list' and similar, since fails for hdu_list = HDUList()
(#417)
Add unit tests for new writeFile functionality.  Also tests the empty HDUList() that used to fail.
(#417)
Clarify the compression options available for writeFits
(#417)
Merge branch 'master' into #417
typo
(#417)
Add recent changes to the CHANGELOG
(#417)
Merge branch 'master' into #417
Merge pull request #418 from GalSim-developers/#417

#417 Fix some errors in galsim.fits.write* functions and documentation