Use Simplecov, Gem::PackageTask, and RSpec in Rakefile

Rcov doesn't work in Ruby 1.9, so I've migrated to SimpleCov.

Jeweler support has been replaced with by using a new :gemspec task
to generate simple-graphite.gemspec and by using Gem::PackageTask for
building new gem files.

The :test functions have been removed and replaced with
Rspec tasks.

A test for hostname validation has been added. This brings coverage
up to 100% on the v1.1.1 codebase.
Use Simplecov, Gem::PackageTask, and RSpec in Rakefile

Closes #7.
Release simple-graphite 2.0.0

* Add support for UDP thanks to Ryan McKern
* Replace jeweler with Gem::PackageTask
* Replace rcov with simplecov