Add default key bindings for OSX.

On small Mac keyboards (the ones that don't have dedicated page up
and page down keys), use Fn+Ctrl+Shift Up/Down instead.

This is not a default keyboard shortcut for Chrome on Mac, but the
following extension uses the same convention:
https://chrome.google.com/webstore/detail/moigagbiaanpboaflikhdhgdfiifdodd
Add ability to move tab to beginning/end.
Update readme for home/end functionality and Mac.
Merge pull request #1 from scentoni/beginning-and-end-keys

Beginning and end keys