Vim CtrlP per directory cache

I use the awesome ctrlp in VIM. At any given point of time I work in multiple directories (git projects). This often pollutes my CtrlP MRU Cache.

For example - I get results for Api directory when I am modifying code in my Web directory. This is midly irritating. To solve this you can set the ctrlp_cache_dir with a prefix of the current directory. Here is a snippet to do that.