enh: added option to set Twig cache, and defaulted to false

Hi,

I had some issues in my workflow where Grunt was watching template files and recompiling them but I did not see the results of my modifications.
It turns out Twig maintains an internal cache of templates and was using the old versions.

So I disabled its cache by default (grunt is a dev tool, so most of the time we should be using the freshest file), with an option to enable it if needed (you never know): options.cache