Test suite for the formatter

[wilzbach]

I couldn't find a place for tests of the formatter. A good start for a test suite would be to parse, and dump a lot of D code with high coverage (e.g. parts of Phobos or Mir) - if afterwards all tests still pass, the formatter didn't totally screw up...

[ghost]

I've added something related here

[WebFreak001]

was fixed in #159