Travis-ci: use cpp environment and test clang

Following changes were made to the travis/shippable builds
* Travis - Use cpp environment instead of python
* Shippable - Added shippable.yml which uses python environment (though Miniconda is used to install python) since shippable does not support cpp
* Use Miniconda to install python (2.6, 2.7, 3.3, 3.4)
* Removed python 3.2 tests as miniconda does not support it.
* Travis - Added a test in clang
* Added `-Wno-constant-logical-operand` flag for Travis/Shippable builds
If this line is not there, the tests fail with 
```ImportError: /home/isuru/miniconda/envs/test-environment/bin/../lib/libm.so.6: version `GLIBC_2.15' not found (required by /home/isuru/csympy/csympy/lib/csympy_wrapper.so)```