[git] Add .gitignore to repository

Based on the very useful github.com/github/gitignore repository.

.gitignore

+# Based on github/gitignore
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+*$py.class
+
+# Distribution / packaging
+.Python
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.coverage
+.coverage.*
+.cache
+nosetests.xml
+coverage.xml
+*.cover
+.hypothesis/
+
+# Environments
+.env
+.venv
+env/
+venv/
+
+# editor files
+*.swp
+*.bak
+*.aux
+*.log
+*.nav
+*.out