Enhanced unittest support

See https://github.com/D-Programming-Language/dmd/pull/3518 for much more details.

### Default druntime tester ###
Updated to ignore ```@disabled``` tests and use the new format.
The tester now runs all tests in a module, even if a previous test failed.

### Example test runner ###
Simple example: http://dpaste.dzfl.pl/56697348500c
Output: http://dpaste.dzfl.pl/c0c706b0cea4

Parallel runner: http://dpaste.dzfl.pl/cef0a42936d6
Output: http://dpaste.dzfl.pl/d2445d87a9d7

### See also ###
DMD pull request:
https://github.com/D-Programming-Language/dmd/pull/3518