Release 3.0.0

Backwards-incompatible changes:

* Make sure plugin_conf_dir is not world readable
* Full rewrite of the network plugin
* Rewrite of postgresql module to allow invocation by defined types

Summary:

Features:

* Varnish plugin improvments
* Add the ability to customize package name.
* Add write_http plugin
* Add statsd plugin
* Add plugin logfile
* Add curl plugin
* Add support for sensors plugin
* Add support for perl plugins
* Allow custom Include directives
* Add valuesabsolute and valuespercentage to df plugin

Bugs:

* Issue 164: syslog plugin needs to be loaded as first plugin
* notify the collectd service when purging plugins
* add collectd-rrdtool package needed for RedHat
* sort python.conf options hash