lib/colors: support schemes customization

 * parse terminal-colors.d/*.scheme files, expected format is

    <name> <color-sequence>

 * supported color sequences:

     - color name (e.g. "red")
     - dir_colors compatible xx;yy (e.g. 01;31) where the sequence may
       contains control chars like \e \a  ..etc.

 * scheme is parsed on demand

Signed-off-by: Karel Zak <kzak@redhat.com>
libsmartcols: use new colors API

Signed-off-by: Karel Zak <kzak@redhat.com>
hexdump: use new colors API

Signed-off-by: Karel Zak <kzak@redhat.com>