Added web hooks functionality

This commit includes:

 * Projects can have zero or more WebHooks.
 * The PostReceive job will ask a project to execute any web hooks defined for that project.
 * WebHook has a URL, we post Github-compatible JSON to that URL.
 * Failure to execute a WebHook will be silently ignored.

spec/models/web_hook_spec.rb

@@ -0,0 +1,54 @@
+require 'spec_helper'
+
+describe WebHook do
+  describe "Associations" do
+    it { should belong_to :project }
+  end
+
+  describe "Validations" do
+    it { should validate_presence_of(:url) }
+
+    context "url format" do
+      it { should allow_value("http://example.com").for(:url) }
+      it { should allow_value("https://excample.com").for(:url) }
+      it { should allow_value("http://test.com/api").for(:url) }
+      it { should allow_value("http://test.com/api?key=abc").for(:url) }
+      it { should allow_value("http://test.com/api?key=abc&type=def").for(:url) }
+
+      it { should_not allow_value("example.com").for(:url) }
+      it { should_not allow_value("ftp://example.com").for(:url) }
+      it { should_not allow_value("herp-and-derp").for(:url) }
+    end
+  end
+
+  describe "execute" do
+    before(:each) do
+      @webhook = Factory :web_hook
+      @project = Factory :project
+      @project.web_hooks << [@webhook]
+      @data = { before: 'oldrev', after: 'newrev', ref: 'ref'}
+
+      WebMock.stub_request(:post, @webhook.url)
+    end
+
+    it "POSTs to the web hook URL" do
+      @webhook.execute(@data)
+      WebMock.should have_requested(:post, @webhook.url).once
+    end
+
+    it "POSTs the data as JSON" do
+      json = @data.to_json
+
+      @webhook.execute(@data)
+      WebMock.should have_requested(:post, @webhook.url).with(body: json).once
+    end
+
+    it "catches exceptions" do
+      WebHook.should_receive(:post).and_raise("Some HTTP Post error")
+
+      lambda {
+        @webhook.execute(@data)
+      }.should_not raise_error
+    end
+  end
+end