Better precompiler support

[LecrisUT]

If we use default compilers, they will call the native precompiler automatically. It would be good to include better support for these:

• #include support. Navigate, auto-complete and parse content.
• #ifdef, etc. support. Already seems to be included, but sometimes it missbehaves, e.g. nested #ifdef
• Macro support. Color scheme, substitution, parsing from cmake variables

[mehrpay]

I'd like to add this to this issue:
Lines that start with !DEC$ are also currently detected as comments. These are compiler modifiers as well, similar to #if() in C++.
Simply showing them with a different color than comments makes it a lot easier to read the code.