Remote pytest and sphinc from install requires

[jaywink]

Including these install a lot of dependencies which are not needed for actually using the library. I would like to propose putting them in extras instead so they can easily be installed in a development environment using:

pip install -e .[dev]

This is the difference:

$ pip install -e .
Successfully installed PyLD-0.7.2 activipy

VS

$ pip install -e .[dev]
Successfully installed Jinja2-2.9.6 MarkupSafe-1.0 Pygments-2.2.0 activipy alabaster-0.7.10 babel-2.4.0 docutils-0.13.1 imagesize-0.7.1 py-1.4.33 pytest-3.0.7 pytz-2017.2 requests-2.14.2 snowballstemmer-1.2.1 sphinx-1.5.5

In a production system all those extra packages are not very nice :)

This does however create a problem with the console scripts. Is there a reason the test client needs to be installed via a package?