Integrate Google Test and port all tests in `testeverything`

This PR is the work on #10 as per discussed at https://github.com/numenta/nupic.core/issues/10#issuecomment-53845038 , using the Google Test framework . Replaces #150 . 

@rhyolight , @ Ready to review and merge.

This PR completed the following tasks:
  * [x] generate JUnit-style report for `nupic.tools` to consume as the original #10 requests
  * [x] porting original tests in `testeverything` with minimal modification
  * [x] silent gcov so it will not generate long outputs to console

Nice-to-have TODOs:

  * decide a goal name for unit test, for now I'm using `tests_unit`
  * decide where the tests go, for now I've moved from `src/test/testeverything` to `src/test/unit`