Enable coverage statistics

[wilzbach]

I copied the .travis.yml from Phobos over and kept the code style bits. For the simple style checks there exist regexes that can be applied in future work, see e.g. dlang/phobos#4385 and enabling Dscanner is also an open task (volunteers wanted!).

Other open tasks for future work:

• coverage of the separate test files isn't included at the moment. While it is possible to set the coverage directory with dmd_coverDestPath, a global way to set the coverage destination dir is missing. Maybe we can add a CLI flag to DMD and modify the common.mak or has anyone a better idea?
• coverage for 32-bit - can we simply run with -m32 on Travis?
• coverage for more platforms (codecov-bash should be run on the AutoTester too)

edit: a preview of the coverage view can be found here

[codecov-io]

Current coverage is 73.93% (diff: 100%)

No coverage report found for master at 51913a6.

Powered by Codecov. Last update 51913a6...afeeedf

[WalterBright]

Auto-merge toggled on