Add 'pollinterval' option, defaulting to 500 (ms).

This significantly speeds up polling time from the default 30 seconds.

Bump version.
Add suppressrefresh option.

This configures whether updates are sent if a value didn't change, and
defaults to true (do not send updates).  Bump version.
Merge branch 'master' of https://github.com/jperkin/node-openzwave
Note libudev-dev requirement on Linux.

Fixes jperkin/node-openzwave#22.
Merge branch 'master' of https://github.com/jperkin/node-openzwave