Simplify introductory documentation.

As a newcomer, I'd like to see just the minimum amount of work required to use
the library. Additional examples and enhancements should be put in a different
paragraph, if pertinent.
Release 2.2.1

Updates CHANGELOG and gemspec for a new release.

Signed-off-by: Ken Barber <ken@bob.sh>
Merge branch 'release_221'

* release_221:
  Release 2.2.1
Merge pull request #20 from stefanozanella/simplify_readme

Simplify introductory documentation.