Provide access to more direct text styling functions

External editing features require some direct access along side the
eventing mechanism currently exposed. Additionally, there are more formatting
options available than DirectTextStyler supports in native functions.

By allowing access to the underlying function used to perform cursor
styling, external editors can easily provide support for custom text style
features (e.g., background colours etc.).
Merge pull request #131 from peitschie/direct-styling-tweaks

Provide access to more direct text styling functions