New .gitignore file to make Git ignore backups and compiled Python code

- *~ makes Git ignore backup files created by editors like Emacs and Gedit.
- *.pyc makes Git ignore for example __pycache__/svtplay_dl.cpython-33.pyc
  Since the __pycache__ directory is now considiered empty, it is also ignored.
Merge pull request #19 from antoneliasson/master

Ignore backup copies and compiled Python code in VCS