New examples page

This is a first attempt at reworking the examples page to allow dynamic loading of examples for all languages. There may be some styling to do to make the whole thing prettier (or at least less messy).

[Online version here.](http://golmote.free.fr/prism-examples/examples.html) (Available examples exist for Markup, CSS, JS and Rust)

(This PR is not meant to be merge in its current state.)

What do you think ?