Revamp documentation

[chmltn]

The documentation is in need of a revamp. This is an issue tracker for said revamp.

Included in this revamp:

• New theme, including a modified page layout
• A rewritten installation and quickstart page
• A new home page and toc structure
• A new tutorial, featuring best practices for creating a telegram.py bot
• A new set of guides for achieving specific things with telegram.py

Current progress on the new documentation can be seen on the revamped-docs branch.