Add support for Python3

[pwittich]

Add support for python3, while maintaining support for python 2. This code requires python3 > 3.6.

The biggest changes are

• change in how zip is handled, especially for when iterating over lists that change
• changes in how lambda functions are handled with tuple arguments
• adapt all uses of print to print() (from __future__ import print_function)
• ensure that all integer division is the same (from __future__ import division)
• other somewhat mysterious import that the interwebs tell me is needed (from __future__ import absolute_import)

I compared the output of the following command between python 2 on the master branch and python 2 and 3 on this branch and diff'd the files. No difference.

./generator_hdl.py ~/src/firmware-hls --uut TC_L1L2E -u 1 -d 0  --no-graph

This is probably not exhaustive; anyone have other tests I should run?

I didn't check the root stuff in python 2 or 3 since I don't have that on this machine.

I also added a github action to test if newly added code is compatible with python3 or not, to ensure we don't have any regression.

[pwittich]

I also tested

./makeReducedConfig.py --no-graph

on master with py2 and on this branch with py2 and py3. No difference for the reduced_* files.