Add support for HTTP transport (connector and Rack server)

[tlrobinson]

No description provided.

[rtyler]

Changing this to:

def initialize(options={})
 # ...
end

Would allow running this a little more cleanly inside of a config.ru, .e.g:

require 'rubygems'
require 'rack'
require 'protobuf'
require 'protobuf/rpc/servers/http/server'

require 'my/rpc'

map '/' do
  run Protobuf::Rpc::Http::Server.new
end

[rtyler]

Largely looks good, but definitely needs some RSpecs added to validate that things will continue to work properly

[tlrobinson]

Updated with suggested fixes and initial HTTP connector specs. Still needs server specs.

[tlrobinson]

Updated with spec/lib/protobuf/rpc/servers/http/server_spec.rb

[rtyler]

I think there's more improvements that can go into this code, but let's merge it and keep on truckin'