Initialize

Publishes basic Firefox plugin for adding links to Instapaper.
Includes proper README and attribution.
Add alt+ctrl, alt+shift, cmd+ctrl and cmd+shift modifiers

Now you can use combinations of modifier keys as Paper modifiers. That
can be useful when you don't want to lose Firefox default modifier
functionality.
Define Paper functions right in exports object
Add notifications on success and right-click option

Requested via e-mail. Both added features are off by default, but can be
enabled in settings pane.
Fix Facebook URLs, fixes the bug reported via e-mail

Facebook prefixes URLs inside the site with facebook.com/l.php?u= to
redirect to the page that warns you about possible dangers ahead.

Before sending URL to Instapaper we need to get rid of this prefix first.