* 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
* Require in Makefile that everyone use bundle to remove inconsistencies
* Require in Gemfile that everyone use Jekyll 1.3.*
* Require in Gemfile that everyone use Ruby 2.0.0 (already used by
Travis and most developers)
* Remove workaround _plugin/svg.rb which showed SVG files in `jekyll
serve` (fixed in Jekyll 1.0.0)
* Remove inconsistent file path workarounds in _plugins/autocrossref.rb
and _plugins/inline-template.rb
