Adding highlighting for string interpolation inside double-quoted strings and character literals inside single-quotes.
Avoiding string interpolation in the form of $var as this is considered bad practice.
Updates to address these comments:
"I still dont quite see why we need to introduce all those options, especially with names that dont say anything about kotlin. I would expect a single kotlin_static_words option to be enough.
Similarly, a single highlighter should be enough here."
