parameterize template for email, autoremove, and autoreboot
Change attributes to use dash, not underscore

The README documents the attributes as unattended-upgrades,
which matches the cookbook name, but the actual attributes
had been written as unattended_upgrades, which could be confusing.

This commit converts them all to dash to match README and the name.
Merge pull request #1 from dagolden/master

Change attribute names to match cookbook name and parameterize more configuration options, including email