update attribute namespace to match cookbook name:

* `new_relic` -> `newrelic-sysmond`
add `sensitive` option to config file template:

* this prevents leaking the license key to `stdout`
* add spec expectation for config file notification
drop support for Chef 10:

* use of the `sensitive` options requires Chef >= 11.13
add `package_action` attribute to support upgrades
Merge pull request #24 from phlipper/v2

Breaking changes for cookbook version 2