Including both piwheels and pypi in Pipfile caused hash mismatches,
which caused installation to fail. I've removed pypi, but this may
break installation on other platforms.
I may need to duplicate Pipfile and Pipfile.lock, one for Pi and
one for non-Pi platforms.
I can confim this commit installed successfully on a Pi.
More or less everything is now done by setup.py
Pipfile simply installs the module in editable mode, which
recursively resolves dependencies as defined in setup.py.