I decided to refactor how the theme module works. The idea is, that I
wanted originally a module that I could give a base16 scheme name to,
and use that globally in my config. However, scheme only took the base16
scheme name without any checks, which was pretty bad. I ended up
creating a new option, schemeName, that scheme is computed from. It then
makes the whole configuration cleaner, and avoids long inputs
interpolations with the scheme name.
