Add an option to load crayon_js at footer.

Crayon js can be put at the bottom of blog pages for better rendering performance. More information at Google Pagespeed Insights: https://developers.google.com/speed/docs/insights/BlockingJS

Crayon does rendering after document.ready, so it is safe to move to the end of the page.

The diffing seems not correct. Use ?w=1 in the url to ignore whitespaces, if you see whole file gets changed.