[Breaking] Expect a global.Promise object

[Whoaa512]

This is a breaking change since the library will now expect a Promise object to be available in the global scope.

Alongside this change:

• update to the travis yaml so we test on the correct platforms
• consolidation to a single entry point since that are virtually the same now
• Update the package.json to reflect the new single entry
• Add a prepublish step to ensure the right code goes out at publish time

Closing #64 #66 #67 in favor of this PR

[rhys-vdw]

Going to merge and release this when I get a chance.

[rhys-vdw]

Thanks @Whoaa512, just released 0.7.0