feature: Color type and syntaxes

[Mwexim]

This pull request yet again adds syntaxes described in issue #40:

• A new Color class that stores colours based on their RGB value (but the stringify-method will present it as HEX). This means that the storing of colours is done through RGB but the actual parsing and displaying is just a HEX.
• Color type with parsing and displaying. Currently, the literal parser uses the '&' symbol (instead of the regular '#') to parse colours since hashtags are occupied for comments already. I was thinking about something like 0xffffff or xffffff (or even x_ffffff) as alternatives. But currently, it'll be something like &ffffff.
• Added ExprColorValues and ExprColorFromRGB (these classes speak for themselves).
• Added support for several literal colours like yellow, lime, maroon, ...

Lastly, I fixed an issue where the Type type was omitted for some weird reason, resulting in the ExprParseAs to not be usable.

I know the current design is a bit sloppy right now, so please let me know any improvements design-wise and coding-wise.

[Olyno]

Interesting features 😃 I think it can be improved 😉