vg_load_colormap() - load a colormap

  int vg_load_colormap(const char * clm, char * vclm, size_t vlen)

  Loads a colormap from the VgaGames-install-directory /usr/share/vgagames
  or from the local directory share/ of your game.

  As in Understanding colormap mentioned, the color of a pixel
  is defined via a color-index, which refers to an entry to the actual colormap.
  When another colormap is loaded, the color-index may reference to another
  color, which results in a global change of the colors.

  E.g. the color-index 28 refered in the first colormap to: 10 0 10,
  but in the second colormap to: 45 30 0,
  then all pixels with color-index 28 of all current bitmaps change their
  color from 10 0 10 to 45 30 0.

  The argument clm is the filename (without path) of the colormap
  to be loaded or just RGB256 for the shipped default colormap
  or GREY256 for the shipped default Grey-colormap.
  At first this file will be searched in "share/" of your game, then
  in the VgaGames-install-directory "/usr/share/vgagames".

  The argument vclm is an address to a buffer to which the function
  returns the previous loaded colormap-file for restoring purposes
  or it is just NULL.
  The function does not write more than vlen characters into vclm
  (including the trailing '\0').

  If it succeeds, it returns 0.
  If an error occurs, it returns -1, giving out an error message to stderr.

  Understanding colormap