Add TOML highlighting support

Tried my best to add TOML support. Everything is there except for multiline string handling, i.e ```toml bigString = """ this is a multi line string """ ``` After some investigation and experimentation, it seems that when doing multiple `'''` or `"""` while also switching between two block states, it will just fail silently (at least I couldn't find where it stopped trying to render). The `highlightStringLiteral` function seems to clash but even disabling that in `TOML` mode, I sill encountered this issue.