Refactor the package to be compatible with Meteor 0.6.5

* Move package source into plugin subdirectory
* Use Npm dependencies for jade and StringScanner, remove submodules
* Add README note for usage with pre/post Meteorite 0.6.0
* Bump version to 0.2.8

This makes the package usable with plain Meteor if installed with
Meteorite 0.6.0 or newer.

Includes a patch from @terro, which was unfortunately never pull
requested.