DDLSHELL-26. Fix incomplete classpath quoting.

Signed-off-by: Aaron Kimball <aaron@wibidata.com>
Initial presentation of SPI.

* Add ParserPlugin and ParserPluginFactory.
* Environment maintains a list of loaded plugins.
* DDLParser is extended to check plugins for syntax matches.
Add SHOW MODULES command.
Add dummy plugin.

The MyPlugin / MyFactory pair responds to "meep" as equivalent to SHOW INSTANCES.
Add 'MODULE <modulename>' command.
Add package-info.java.
Add parser plugin test kit.
Add audience annotations.
Add unit tests for plugins.
Remove sample plugin used for shell testing.