Merge pull request #415 from GalSim-developers/#377

#377 Add options to use a larger range of k values when building grid for PowerSpectrum
removed warning re: more than one size param from Airy, since it only has one anyway
documentation typos
Switch from std::isnan to boost::math::isnan #378
merged in master, fixed trivial conflict
(#340)
Merge branch 'master' into #417
typo
(#417)
Add recent changes to the CHANGELOG
(#417)
Merge pull request #416 from GalSim-developers/#340

#340 Speed up HSM code
Merge branch 'master' into #417
initial mods: changelog and base.py
(#420)
initial mods: SBSersic.cpp, SBSersic.h
(#420)
conversion of r0 to hlr included (some boost linking issues remain)
(#420)
An uncertain boost::python bug fix, on specifying base classes
(#420)
Remove image.at(pos) from python, since it seems to be causing help(ImageD), etc. to hang (or crash) #421
bug fix, and some debug messages
(#420)
Merge pull request #418 from GalSim-developers/#417

#417 Fix some errors in galsim.fits.write* functions and documentation
Merge branch 'master' into #420
update base.py so that it knows of getScaleRadius()
(#420)
image arithmetic overhaul: add, sub, mult, div, and in-place versions
(#419)