Add programatic cache save

[theKashey]

A very useful project, so widely used. With one flawn - cache is stored only on the graceful project exit.

I was trying to speed up the load times of my dev server, the one I always ctrl+c in order to close, and after hooking into the cache internals found that cache was just missing. It was never dumped on the disk.

I've added one export to the package, letting myself store cache when I want to save it (after server start), and was able to utilize the power of caching for the first time.

Feature request

Expose saveCache API for applications with never-ending or self-controleld life cycles.