Updating the jruby-rack jar to 1.1.12
Removing the old jruby-rack jar.
Reproduce issue4 - ERR_CONTENT_LENGTH_MISMATCH
Merge pull request #4 from erdeszt/jetty-rackup-update

Updating the jruby-rack jar to 1.1.12
Switch from jeweller to pure bundler for gem packaging
Update the README, update links
Fix deprecated `include_class`
Packaging, including the main jetty-rackup, works
Add support for `Host` option as suggested by erdeszt