Android Plugin authoring guide uses <plugin> instead of <feature>

See http://cordova.apache.org/docs/en/3.0.0/guide_platforms_android_plugin.md.html#Android%20Plugins

Do a search for "<plugin"

We should document <feature> instead, and also document <param> elements properly.

This relates to CB-4293.

Also: the link to CordovaPlugin.java at the bottom of the document is broken.