This commit removes the old parser, the deprecated parser module, the old parser compatibility flags and environment variables and all associated support code and documentation.
- Switch from getopt to argparse.
- Removed the limitation of not being able to produce both C and H simultaneously.
This will make it run faster since it parses the asdl definition once and uses the generated tree to generate both the header and the C source.
* Update the source path of the pegen target within the Windows regen project.
Change the path to Windows path formats.
* Use the more reliable SetEnv task for Cpp Projects in MSBuild.
