Support for Markdown, Kotlin

[tferr]

This relates to scijava/pom-scijava#191

The new RSyntaxTextArea components have built-in support for Kotlin and Markdown syntax (see release notes). Would be awesome to add support for those here.

@imagejan, @haesleinhuepf: You guys implemented LanguageSupports in the past. I'm confident it would be trivial for you to tackle this, so pinging you in 😉

I guess one could also make available syntaxes for common stuff like XML or JSON, that once in a while are present in Fiji. @ctrueden , agree?

[tferr]

Closing, since this has been partially implemented in #64