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/workers/post_receive_spec.rb

@@ -0,0 +1,26 @@
+require 'spec_helper'
+
+describe PostReceive do
+
+  context "as a resque worker" do
+    it "reponds to #perform" do
+      PostReceive.should respond_to(:perform)
+    end
+  end
+
+  context "web hooks" do
+    let(:project) { Factory :project }
+
+    it "it retrieves the correct project" do
+      Project.should_receive(:find_by_path).with(project.path)
+      PostReceive.perform(project.path, 'sha-old', 'sha-new', 'refs/heads/master')
+    end
+
+    it "asks the project to execute web hooks" do
+      Project.stub(find_by_path: project)
+      project.should_receive(:execute_web_hooks).with('sha-old', 'sha-new', 'refs/heads/master')
+
+      PostReceive.perform(project.path, 'sha-old', 'sha-new', 'refs/heads/master')
+    end
+  end
+end