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 (@rhyolight , @scottpurdy , @chetan51), using the Google Test framework . Replaces #150 . 

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
  * [ ] add tests for the re-implemented `Tester` 

Decision 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`
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