FEATURE: multithreaded approach to gather metrics from multiple nodes

- thread processing model
 - construction of configuration for each thread done
 - thread aware signal handler
- read configuration for munin-node hosts from file
- optimize way how to get plugins from hosts (do not read it every time)
- filter list of plugins according to supplied regexp
- handle signal for list of plugin reload
- syslog logging instead basic one
- extended documentation in README.md