Format function calls as code in prose.
Add some simple docblocks for PredisCache.
Document requirements in a bit more detail in README.

It's easier for users to read through the requirements in prose than to
have to parse the composer.json specification.  This makes things a bit
friendlier for viewing.
Fix the primary header to be project name.

This makes things more like our standard used in other projects and
removes the duplicated info from right below the badges.
Merge pull request #12 from nubs/master

Update documentation from review