BLD: Updated requirements.

The UTP pseudopotentials need scipy. The requirements file has now been
updated.
DOC: Improved installation instructions.
BLD: Added information on how to make a release.

Mostly meant for my (and other developers in the extremely unlikely
event that we get any) benefit.
BLD: docs/source/conf.py gets version number from __init__.py

This should prevent having conflicting version numbers between the docs
and the code. This does mean contactpp needs to be installed before
re-building the documentation following a version change.
REL: Release v1.1.