Support Phoenix 1.3+ project structure

[c-brenn]

Phoenix 1.3 has been released, including significant changes to the structure of Phoenix projects.

We will need to update the Projections and gf binding to accommodate these changes (there may be more changes that I can't think of atm).

In terms of supporting both Phoenix 1.3+ and pre 1.3; I think we can tag the current version of the plugin and add documentation to the readme instructing people using older versions of phoenix to install that specific tagged version of the plugin.

Those using Phoenix 1.3+ will install the plugin as normal.