pymake + python 3 patches

Fork of https://github.com/mozilla/pymake with additional patches for Python 3, breaking Python 2 support.

What is pymake?

make.py (and the pymake modules that support it) are an implementation of the make tool which are mostly compatible with makefiles written for GNU make.

Please refer to ORIGINAL_README and LICENSE

Build status:

Platform	Python	CI Status
linux	3.7.x
osx	3.7.3	as above -- same ci build as linux.
windows	todo	todo

Development - how to run the test suite:

Prerequisites:

• default python is Python 3
• pytest installed (pip install -r test-requirements.txt)
• a dev install of pymake package in this repo (pip install -e .)
• GNU Make installed to test against (assumed to be named gmake, can be overridden)

With pytest installed, the test suite can be run from the root directory of this repo as follows:

pytest --gmake=make .

With the optional pytest-dist plugin installed, the tests can be run in parallel. For example, to use 8 CPUs:

pytest --gmake=make -n 8 .

This gives about a 5x speedup on my machine.