Merge pull request #7 from kumar303/example

Adds example app (bug 981231)
Document public API (bug 981230)
Merge pull request #8 from kumar303/docs

Document public API (bug 981230)
Fix mozPay error handler (bug 982867)
Always run tests against Firefox

This is still pretty fast compared to Phantom and Travis CI
supports it so, hey, why not.
Add receipt to device on purchase (bug 981233)
Merge pull request #9 from kumar303/receipt

Add receipt to device on purchase (bug 981233)
Mention how App error strings are passed through
Use new prepare inapp API url (bug 981232)
Merge pull request #10 from kumar303/urls

Use new prepare inapp API url (bug 981232)
Complain if not installed as an app
Made the example app link more prominent
Fixed up example app for local development
Whoops. Send URL encoded post data.
Force an empty build dir
Remove node_modules from example app
Turn example into packaged app
Merge pull request #11 from kumar303/packaged

Turn example into packaged app (bug 1014841)
use a custom profile in Firefox OS Simulator
Hard-coding this product ID.

Hmm, this needs to be configurable.