some preparations for tagging v0.5
(#439)
Revert "some preparations for tagging v0.5"

This reverts commit 1d50549ef4d42f404ee6f9fef17062636eb811cb.
merged in master, updated to v0.5.1 with changes in this branch
(#439)
Put back a CHANGELOG item Rachel accidentally removed
(#439)
fixed error in MeasMoments: missing hsm
(#439)
Use Barney's suggested wording for offset doc.
(#439)
Clean up docs a bit.  Specifically remove references to the SB* classes that users don't know anything about.
(#439)
Merge branch '#439' of github.com:GalSim-developers/GalSim into #439
typo
(#439)
Merge pull request #448 from GalSim-developers/#439

#439 A bunch of fairly small changes
Merge branch 'master' into #389

Conflicts:
	CHANGELOG.md
	galsim/optics.py