Implement AMD compatible version of include_gon

include_gon_amd renders a script tag which uses define() to define a
module. The name of the module is the given namespace and defaults to
'gon' if none given.
Update Readme to introduce include_gon_amd
Merge pull request #156 from vijoc/amd

Adding include_gon_amd, an AMD compatible version of include_gon