We're going to move the executable's here (or at least those that part
of the core library). The 'sphinx-build' executable was already moved,
so lets do 'sphinx-quickstart' next.
To avoid breaking packages that are using this feature directly, aliases
for the old 'main' method are included. This is based on what Django
does [1] and, like Django, will allow us to safely remove the old
modules in Sphinx 2.0.
[1] https://github.com/django/django/blob/1.11/django/test/runner.py#L688-L695
Signed-off-by: Stephen Finucane <stephen@that.guru>