Add gas giant texture for randomly generated planets
Make randomly generated planets rotate along orbit's axis

It seems natural that planets have rotation axis in the same direction
as the orbits.  We don't really know much about solar system formation
process, but at least angular momentum must be conserved.
Make Astrobj::absmag accessible from Squirrel scripts

Also assigned decent default values for Alpha Centauri and random
stars' absmag.
Add Rigil Centaurus B b, actual planet candidate to space_debug.ssd

It has about the same mass as the Earth, but not likely habitable
since it's on much closer orbit to the star.  The planet's surface
is speculated to be molten rock ocean.  Its orbital elements are
not accurate.

Rigil Kentaurus B a might be better deleted since there's no such
naming convention which gives "a" to a extrasolar planet in astronomy.
Make FindBrightestAstrobj capable of returning multiple Astrobjs

There could be multiple stars that illuminate planets in a binary
solar system.  We need a way to obtain a list of brightest Astrobjs
instead of just one.  FindBrightestAstrobj can do this by passing
more than 1 to resultCount.
Make DrawTextureSphere work with multiple lights

Now you can see a planet in a multi-star solar system lit with
multiple lights.