Emacs mode improvements

* Font locking (colorization)
  - all keywords for statements and blocks are now recognized (but not option names)
  - MATLAB-style (single-quoted) strings now recognized
  - improve handling of macroprocessor (but multiline macro commands/exprs not
    yet working)
  - recognize mathematical functions and constants (nan and inf)
  - highlight the pound-sign for model-local variables

* Indentation
  - basic indentation within blocks (offset customizable through option)
  - more elaborate indentation (e.g. multiline equations or statements) not yet
    working