* Move all scripts and documentation to Python3
Python 2 EOL is Jan 1, 2020. Migrate scripts to run under Python 3.
Under Windows, we're already running Python 3.7, by dumb luck. The
oddness is that the Windows standalone executable for Python 3 is called
"python" whereas under UNIX-like OSes it's called "python3" with
"python" always referring to the Python 2 executable. The ZIP needs to
be updated to include a Python3.exe (copy of Python.exe) so that we can
use the same command lines under Linux and Windows, and to preserve my
sanity.
Fixes#6376
* Add new Windows ZIP with python3.exe file
* Sort options in boards.txt generation for repeatability
The order of the board opts dict changes depending on the Python version
and machine, so sort the options before printing them to get a stable
ordering.
* Re-add Python2 compatibility tweaks
Most scripts can run as Python 2 or Python 3 with minimal changes, so
re-add (and fix, as necessary) compatibility tweaks to the scripts.
Using espota.py as a module by calling espota.main(args) was not working because the args given to main were not being passed into parser.parse_args(). I fixed this by having main pass args to the parser function, which in turn passes them to the parser object's parse_args() function.
randomization is good in cases where the previous port is not yet
released by the OS or the server hangs
On OS X it's very noticeable if you need to OTA twice in a short time.
Proper error handling in the uploading python script
Much faster OTA example sketch with better results
New Update class that simplifies updating the firmware from any source
Updated Esp.updateSketch() to use the new class
