Adds monolog, updates requirement versions, removes slim/extras
Removes Slim logging in favor of Monolog. Fixes #6.
Updates links, replaces Slim Extras section with Slim Views section.

Related to #6.
Adds note about ensuring `logs/` and `templates/cache` are web
writeable.
Merge pull request #7 from jeremykendall/feature/monolog

Removes slim/extras and replaces Slim logging with Monolog