Moved `test/coverage` to `test/coverage/lcov`.
Added support of `gcovr`.

* test/coverage/jamfile: Newly added. Brought together the definition of
  `NOARCH_PROPERTIES` global constant into this file.
* test/coverage/lcov/jamfile: Moved the definition of `NOARCH_PROPERTIES` to
  `test/coverage/jamfile`.
* test/coverage/gcovr/jamfile: Newly added.
* test/coverage/gcovr/.gitignore: Newly added.
Merge pull request #4 from Cryolite/feature/gcovr

feature/gcovr