Trying out removing the memory mapper.

Never use it. Don't know anyone who does. So it's just unessesary maintenance.
Updating docs to match the code and how we use minimapper.
Making the intro text shorter.
Making it even shorter.
More work on docs.
Merge branch 'simplify'
Upping version. This change changes the mapper class name and removes
the in-memory mapper.
Update gemspec.
Cleanup docs
Simplify docs