Parameterize configuration ownership

This commit adds class parameters for the 'owner' and 'group' properties
of the config file. This allows this module to manage the configuration
in other Puppet installations such as Puppet Enterprise.
Tidy up documentation

- Documentation refers to TCP port 5959, code defaults to 5999.
- s/apache/logstash_reporter/ in init.pp
Lowercase and _-separate metric names
Format start and end timestamps as ISO8601
Merge branch 'pr/5'

* pr/5:
  Tidy up documentation
Merge branch 'pr/4'

* pr/4:
  Parameterize configuration ownership