Fixes for recent python 3 versions

[uweschmitt]

Hi Joel,

this also includes changes to use gitlab-ci as I was assuming that hope would be hosted on cosmo-gitlab.phys.ethz.ch where we decided to use gitlab-ci. I can create a pull request only with the modifications related to Python 3 versions if wanted.

Best
Uwe

[jakeret]

The new numba dependency in the requirements.txt seem to cause some problems on travis

  Running setup.py install for llvmlite ... error
    Complete output from command /home/travis/miniconda/bin/python -u -c "import setuptools, tokenize;__file__='/tmp/pip-build-53w7uxop/llvmlite/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record /tmp/pip-sywh38cm-record/install-record.txt --single-version-externally-managed --compile:
    running install
    running build
    got version from file /tmp/pip-build-53w7uxop/llvmlite/llvmlite/_version.py {'version': '0.20.0', 'full': '9ee27e85786ac3b23d32c0e5d844f1157e69df37'}
    running build_ext
    /home/travis/miniconda/bin/python /tmp/pip-build-53w7uxop/llvmlite/ffi/build.py
    LLVM version... 3.9.0
    
    Traceback (most recent call last):
      File "/tmp/pip-build-53w7uxop/llvmlite/ffi/build.py", line 141, in <module>
        main()
      File "/tmp/pip-build-53w7uxop/llvmlite/ffi/build.py", line 131, in main
        main_posix('linux', '.so')
      File "/tmp/pip-build-53w7uxop/llvmlite/ffi/build.py", line 105, in main_posix
        raise RuntimeError(msg)
    RuntimeError: Building llvmlite requires LLVM 4.0.x. Be sure to set LLVM_CONFIG to the right executable path.
    Read the documentation at http://llvmlite.pydata.org/ for more information about building llvmlite.
    
    error: command '/home/travis/miniconda/bin/python' failed with exit status 1
    

The import sphinx_pynpoint_theme in conf.py seems a bit odd and is most likely not going to work on most of the systems