Vim command line fixes
A color is set if it is not empty and not negative
Handle true colors - closes #1

True colors are handled through vim, not gvim.
This makes synIDattr(code, 'fg#', 'gui') not always output #RRGGBB
codes.
To solve this we use $VIMRUNTIME/rgb.txt, by preprocessing it as a
colorname to #RRGGBB color codes converter.
v1.0.0 - Debian packaging