* Added therubyracer to Gemfile. Without a JS runtime, middleman won't start
* Bumped ruby version from 2.2.3 to 2.2.7
* Simplified how Rakefile calls bundler, per http://bundler.io/v1.3/man/bundle-exec.1.html#Shelling-out
* Updated build instructions to include a step to build yard docs
Changed instructions to use the bundled middleman. It is likely the gem isn't globally installed and it isn't at least if just these instructions are followed.
