Installing with pip in the post PEP 517 era

[mboisson]

Starting with the implementation of PEP 517 in pip 19.x, installing a package from source with

pip install <tarball>

is no longer supported unless one disables PEP 517. This is discussed here:
https://discuss.python.org/t/pep-517-and-projects-that-cant-install-via-wheels/791

The recommended procedure is to use

pip wheel <tarball>

to build a binary wheel which then can be installed using

pip install <wheel>

The PythonPackage EasyBlock will need to be updated to use that procedure when installing through pip.