Add environment variable formatting

Fix setuptools-scm pip requirements.

• {ANYTHING!e}: !e is a special conversion flag for Environment variables. This will
  be replaced with the correct shell environment variable. For bash it becomes $ANYTHING,
  in power shell $env:ANYTHING, and in command prompt %ANYTHING%. ANYTHING is the name
  of the environment variable.
• {;}: This is replaced with the path separator for the shell. Ie : for bash, and ;
  on windows(including bash).