Multiple additions

Here is a summary of additions for the library:

- lib/nagios/config.rb - class for parsing nagios.cfg file. By using this class there is no more  need to specify path to status.dat file. It is detected automatically.
- lib/nagios/objects.rb - class for parsing and manipulating objects configuration (i.e. hosts, hostgroups, services, contacts etc)
- lib/nagios/external_commands.rb - class for using external commands: submit passive checks etc.
- test/data - sample nagios configuration files to be able to run tests in 'offline' mode, i.e. on the server where Nagios is not installed.