Build NVDA with Python 3.8 32-bit (#12042)
* SConstruct: specify Pyhton 3.8.
* SConstruct: remove Python 3.7.6 check.
The latest version of Python 3.7 is 3.7.9 (as of February 2021). Therefore remove 3.7.6 check.
* SConstruct: update copyright year
* SCons.bat: run SCons under Python 3.8 (32-bit).
* Revert "SConstruct: update copyright year"
This reverts commit 096f61b1a3507c4ecc8a1ae5b289c5862c9a9962 due to impending Py2Exe upgrade that will update copyright header.
* scons.bat: update comment
* Readme: mention Python 3.8.
* appveyor.yml: Instruct appveyor to use Python 3.8
Co-authored-by: Michael Curran <mick@nvaccess.org>
