Manually wrap Readme.md

This commit manually wraps long lines in the Readme.md. This will
make it easier to edit in editors that don't do automatic
wrapping (or have it turned off).
Update gitignore

The update adds "*.class" to the gitignore file. The Java REPL
plugin for IntelliJ likes to leave class files laying around the
source tree. So this is the easiest way to avoid them getting
added to the repository.
Add quick demo to Readme.md

This commit adds a short demonstation of how to use the library
to the Readme.md