Add build-essential package for Debian/Ubuntu

rackspace-monitoring depends on rackspace-fog which depends on fog which
depends on nokogiri. Nokogiri needs a working build system to install.

I'm not sure and couldn't find reliable info on what the Redhat/CentOS
equivalent would be so I haven't added that.
Bump version to 0.2.4
Merge pull request #25 from racker/install_build_essentials

Add build-essential package for Debian/Ubuntu