Flake8's INI config file format requires commas after each line. Because our file didn't have them, the exclude list
wasn't set up correctly, and the --extend-exclude flag wasn't working. This PR fixes the .flake8 file.
Also, update flake8 to the latest version available (because version 3.8 is required to get the --extend-exclude flag)
and use the flag to exclude the files in the scripts/ directory from the python2 linter (since the scripts are python3).
This change moves the python code for emsdk into a file ending in .py.
This script is then run via emsdk.bat on windows or emsdk (a shell
script) on non-windows.
This avoid the #!/bin/sh at the top of the python script and the "exec"
hack on the first line that re-runs it under python. Hopefully this
preserves the intent of #273 without jumping through so many hoops.
