Create a cache of code generated by pygments

[csokol]

It would be nice to create a cache of code tags to make the build process of the afc's faster.

We could call pygments directly from tubaina (and drop minted) , or create a wrapper of pygments which would be called by minted.

This cache could be placed at ~/.tubaina/codecache/ and each time you need that code you should check a hash from that code and verify if there is already a file for that at the cache dir.