Time to migrate to Python 3!

[rusefillc]

This repo still uses 2.7 version of Python

We need to pick migration attempts from the internet and combine with our functional fixes

[rusefillc]

Kind of depends #4

[rusefillc]

See also provideyourown#8

[rusefillc]

Extra info:

there are too many gerbmerge forks. There is a fork with python3 but two problem with it

1. that other fork does not have our fixes, so potentially one can PR all needed fixed into https://github.com/jnicolson/gerbmerge

2. overall I am failing to even start https://github.com/jnicolson/gerbmerge see Is this fork trying to be compatible or has unique configuration approach? jnicolson/gerbmerge#10

It could be that the way to go is really to migrate our https://github.com/rusefi/gerbmerge fork to Python 3 as is since that's the safest way to make sure we have all the fixes/changes we need

[rusefillc]

we have manual validation tests in https://github.com/rusefi/gerbmerge/tree/rusefi-tests

See also jnicolson#9

[andreika-git]

andreika-git@f78db83