3.0 - Bump it up!

wxPython recently released their long awaited 4.x line ("Phoenix"). Upgrading to 4.0.1 finally allowed me to provide a macOS binary for High Sierra as I'm no longer affected by pyinstaller/pyinstaller#2355.

At the same time I bumped esptool.py to 2.2.1. That fixed an UART speed limit on macOS (maxed out at 230k).

I also switched to building with Python 3.

Anti-virus reports:

• NodeMCU-PyFlasher-3.0.dmg - macOS bundle (High Sierra)
• NodeMCU-PyFlasher-3.0-x86.exe - Windows 32-bit, built on Windows 7
• NodeMCU-PyFlasher-3.0-x64.exe - Windows 64-bit, built on Windows 10