Unaddressed highlight groups

Hi,

I’ve recently been working on creating an editor for a school project, and wanted to make sure that it has support some popular themes, so I decided to port Dracula.

I found the spec really helpful, but have a few highlight groups that I couldn’t find a colour for:

- Macros
- Pre-processor items (e.g. `#if` in C)
- Character literals (are these classed as constants or strings?)
- ‘Special variables’ (this is something I made up when I created the syntax highlighting for my editor – two uses I can think of are symbols in Ruby and lifetimes in Rust)
- Modules

Thanks!