Adding user option to toggle Antialiasing on/off. Eventually, this will
be set via the Options window, in the Advanced tab. However, that tool
is still not functioning, so for now I am binding it to the "A" key.I had said on the mailing list that I was not going to keep the
integer-pixel draw functions, because they weren't much faster than the
floating-pixel equivalents. After looking at it again, the
integer-pixel draw functions are 20-40% faster than their floating-point
counterparts.

So for now I am going to commit the changes that include
using integer draw functions when antialiasing is off.Also, I have fixed the problem where star colors get saturated when
antialiasing is turned off (this was noticeable before while the sky was
in motion). The problem was caused by the fact that the colored rim of
star images cannot be less than 1 pixel wide without antialiasing. I
solved it by keeping the width at 1 pixel, but desaturating the color of
the rim by an appropriate amount. It works pretty well.Related API change: I removed some arguments from fromScreen() and
toScreen(), because we were just passing around things like
Options::useAltAz(), which are already accessible from within any
function. We still need to pass a "bool useRefraction" to toScreen, but
this should almost always be left at its default value (true), which
actually means "adopt whatever Options::useRefraction() is set to". The
exception is the Horizon; these points must never be refracted, so we
pass "false" to the argument, which means "ignore
Options::useRefraction(); don't refract the point".There's also some code in this commit related to adding XYZ support to
SkyPoint, but nothing yet that you'll notice unless you look at the
code.