Site Docs & Previews: Update Site Building/Previewing Docs

* New plugin: remove-html-extension falls back to /foo.html when /foo
  isn't found in `jekyll serve` mode.

* New Makefile target: `make preview` runs bundle exec jekyll serve

* Updated site docs to describe installing all required dependencies.
  Fully tested using a new install of Ubuntu Server 14.04.1

_plugins/remove-html-extension.rb

@@ -0,0 +1,31 @@
+# This file is licensed under the MIT License (MIT) available on
+# http://opensource.org/licenses/MIT.
+
+# remove-html-extensions is a temporary workaround to allow the built-in
+# Jekyll server to serve files like /foo.html as /foo
+# This functonality is already part of Jekyll 3.0.0beta and this plugin
+# can be removed when we upgrade that far
+
+require 'webrick'
+include WEBrick
+
+## Code starting here taken from https://github.com/jekyll/jekyll/commit/e99a9e5821a7ba16ce42a1f5de378012f22acae0 MIT license
+
+# Custom WEBrick FileHandler servlet for serving "/file.html" at "/file"
+# when no exact match is found. This mirrors the behavior of GitHub Pages
+# and many static web server configs.
+class FileHandler < ::WEBrick::HTTPServlet::FileHandler
+  def search_file(req, res, basename)
+    if file = super
+      file
+    else
+      super(req, res, "#{basename}.html")
+    end
+  end
+end
+
+## End copied code
+
+## Horribly hackish and produces a warning, but it works and avoids us
+## having to modify Jekyll on every end-user system
+WEBrick::HTTPServlet::FileHandler = FileHandler