Added support for base24

[YoloClin]

This commit enables support for 24 colors (aka 'base24' https://github.com/Base24/base24/). It could be modified for 256 colors also.

Unit tests are currently failing due to an issue with template-source repo (See PR https://github.com/chriskempson/base16-templates-source/pull/109 ), the workaround is to use my fork ( https://github.com/YoloClin/base16-templates-source ) for the time being, but I don't plan on maintaining my fork once it has been merged.