Merged some aspects into a unified color scheme.

+ The color file now always sets values for both cterm and gui, instead of
  trying to detect which is being used. This allows, for instance, for
  starting in terminal vim, and using :gui to start the gui without
  having to re-run the color command.
+ The file now inspects the value of &background. If it is 'dark', the
  hybrid palette is used. If it is 'light', the hybrid-light palette is
  used. Choice of palette can therefore be toggled via 'set bg=light/dark'.
+ hybrid-light.vim has been deleted in light of the previous change.