Have setuptools setup.py for serious distribution

This is a) cooler and b) a requirement for deploying it on PyPI.

It removes need of __all__ shit (which is hard to keep updated), and
allows installing instaloader easily as a global module and executable.
Additionally it removes __init__.py.

.gitignore

@@ -1,2 +1,4 @@
 __pycache__/
-.idea
+build/
+dist/
+instaloader.egg-info/