[rtext] Introducing styled texts

[SultansOfCode]

Hello!

I have added the ability to customize text color and background color with special characters inside the text (pretty much like mIRC does)

You can use the functions DrawTextStyled and DrawTextStyledEx almost as you would use DrawText and DrawTextEx respectively

The changes are: instead of passing the Color, you will pass an array of Colors and the size of this array

Inside the text you can use \003 to set the foreground color, \004 to set the background color, \015 to reset them to their default values (first color in array, if any, as foreground color [or black, if none], and transparent background) and \022 to swap foreground and background colors

Also added MeasureTextStyled and MeasureTextStyledEx to correctly measure them as MeasureText and MeasureTextEx would for plain texts

If any adjustment is needed, either to the code or to the PR, please, let me know

Thank you

[raysan5]

@SultansOfCode Thanks for the nice effect! I'm afraid this implementation is too custom to be added to raylib for all users, the styling mechanism should be a user-decision, not imposed by raylib.

Still, it can be directly implemented into a single example intended for users looking for an implementation sample or as a base solution to implement their own.

Please, could you review it to make it self-contained to the example? Also note that examples should follow some guidelines.