Change default codec to "plain"

This matches other logstash input plugins
Add maxFormSize option

Sets the buffer size for forms POST/PUTed to jetty. The default is
200kb. Set to `-1` to disable.
Simplify scanning the POST/PUT body
Merge remote-tracking branch 'issue1/master'

Conflicts:
	http.rb

Resolves #1 - Keep-alive, "host" key for log event
Bump Jetty version to 9.1.5.v20140505
Add Apache v2 LICENSE file
Update README to include new options, defaults

Includes:
- New configuration option maxFormSize
- Addition of LICENSE
- Change of default codec from `json` to `plain`
- Performance considerations section
Merge remote-tracking branch 'upstream/master'