[dist] change the default python command to 'py'

The 'py' command (python launcher) is available since Python 3.3. It is
installed in a PATH directory by default. So it is easier to use than
the 'python' command.

see:
https://docs.python.org/3/using/windows.html#python-launcher-for-windows
[dist] remove an unnecessary include directory
[dist] remove redundant rules
Merge branch 'topic/update-makefile'