Format inside of directives

A suggestion from #193 was to remove trailing spaces in conditional directives.

I think this is a good idea, and could be extended to a more general rule for formatting directives.
They can get pretty complicated so we should be careful in implementing this, but there are at least some simple cases that would be nice to cover.

For example
1. `{$ifdef NAME}`
* normalise casing of the directive (unclear whether lower or upper case is preferable)
* completed in #281
* one space between identifier and directive
* no trailing space
2. `{$COMPILERDIRECTIVE}`
* no spaces after directive
3. `{$if DEFINED(Foo) and (CONSTANT > 3)}`
* a real stretch goal would be to format the `{$if}` directive expressions like a regular Delphi expression