Introduce pytest command as recommended entry point

[davehunt]

It should be possible to run pytest using pytest command in addition to the existing py.test. This resolves a naming confusion that has existed for many years.

Explanation of py.test vs pytest from FAQ:

Some of the reasons are historic, others are practical. pytest used to be part of the py package which provided several developer utilities, all starting with py.<TAB>, thus providing nice TAB-completion. If you install pip install pycmd you get these tools from a separate package. These days the command line tool could be called pytest but since many people have gotten used to the old name and there is another tool named “pytest” we just decided to stick with py.test for now.

The issue with the 'other tool' has been resolved for some time now, so from pytest 3.0 we will supported and recommend use of pytest as the main command instead of py.test. It's possible that in future we will deprecate py.test and potentially even remove it.

[davehunt]

This was fixed in ef9dd14