Add pull requests to irc hook

Add pull request functionality to the IRC service.

In addition, allow the IRC service to use the default ports of 6667 (non-SSL) and 9999 (SSL) if the user doesn't specify.

Tested with this `docs/github_payload`:
```
{
  "data" => {
    "server" => "irc.freenode.net",
    "port" => "6667",
    "room" => "#jeffweiss-test",
    "nick" => "github-jweiss",
  },

  "payload" => {
    "action"  => "opened",
    "pull_request" => {
      "number" => 306,
      "commits" => 1,
      "state" => "open",
      "title" => "(#15596) External facts dirs configurable via environment variable",
      "body"  => "Eliminate command line options for setting external fact directories.
      Configure external fact directories using the environment variable FACTER_LIB.

      Prior to this commit, the external fact directories were either the
      platform-specific hard-coded defaults or, using a single directory,
      passed in via command line option. This commit alters the functionality
      so that it uses an environment variable which can handle multiple paths.

      When ENV[FACTER_PATH] is set to empty string, no external fact dir path
      will be used. When it is not set, the platform-specific hard-coded defaults
      will be used.",
      "user" => { "login" => "Evan-Pierce" },
      "head" => {"label" => "Evan-Pierce:ticket/2.x/15596_ext-facts-configurable-via-env"},
      "base" => {"label" => "puppetlabs:2.x"},
      "html_url"  => "https://github.com/puppetlabs/facter/pull/306"
    },
    "after"   => "a47fd41f3aa4610ea527dcc1669dfdb9c15c5425",
    "ref"     => "refs/heads/master",
    "before"  => "4c8124ffcf4039d292442eeccabdeca5af5c5017",
    "compare" => "http://github.com/mojombo/grit/compare/4c8124ffcf4039d292442eeccabdeca5af5c5017...a47fd41f3aa4610ea527dcc1669dfdb9c15c5425",
    "forced"  => false,
    "created" => false,
    "deleted" => false,

    "repository" => {
      "name"  => "facter",
      "url"   => "http://github.com/puppetlabs/facter",
      "owner" => { "name" => "puppetlabs", "email" => "admin@puppetlabs.com" }
    },

    "pusher" => {
      "name" => "Evan-Pierce"
    },

    "commits" => [
      {
        "distinct"  => true,
        "removed"   => [],
        "message"   => "[#WEB-249 status:31 resolution:1] stub git call for Grit#heads test",
        "added"     => [],
        "timestamp" => "2007-10-10T00:11:02-07:00",
        "modified"  => ["lib/grit/grit.rb", "test/helper.rb", "test/test_grit.rb"],
        "url"       => "http://github.com/mojombo/grit/commit/06f63b43050935962f84fe54473a7c5de7977325",
        "author"    => { "name" => "Tom Preston-Werner", "email" => "tom@mojombo.com" },
        "id"        => "06f63b43050935962f84fe54473a7c5de7977325"
      },
      {
        "distinct"  => true,
        "removed"   => [],
        "message"   => "clean up heads test",
        "added"     => [],
        "timestamp" => "2007-10-10T00:18:20-07:00",
        "modified"  => ["test/test_grit.rb"],
        "url"       => "http://github.com/mojombo/grit/commit/5057e76a11abd02e83b7d3d3171c4b68d9c88480",
        "author"    => { "name" => "Tom Preston-Werner", "email" => "tom@mojombo.com" },
        "id"        => "5057e76a11abd02e83b7d3d3171c4b68d9c88480"
      },
      {
        "distinct"  => true,
        "removed"   => [],
        "message"   => "add more comments throughout",
        "added"     => [],
        "timestamp" => "2007-10-10T00:50:39-07:00",
        "modified"  => ["lib/grit.rb", "lib/grit/commit.rb", "lib/grit/grit.rb"],
        "url"       => "http://github.com/mojombo/grit/commit/a47fd41f3aa4610ea527dcc1669dfdb9c15c5425",
        "author"    => { "name" => "Tom Preston-Werner", "email" => "tom@mojombo.com" },
        "id"        => "a47fd41f3aa4610ea527dcc1669dfdb9c15c5425"
      }
    ]
  }
}


```