Cache built modules

[staltz]

This issue is just an idea or feature request. I may work on it myself if I find the time.

Like node-gyp-cache, it would be good if nodejs-mobile-gyp kept the resulting folder (and version) of a dependency that was built. E.g. ~/.nodejs-mobile-gyp/cache/[email protected] for leveldown version 5.4.1 after the first time this dependency and version are built locally.

Current build times of my nodejs-mobile project are about 11min because of native modules, it would be great to bring that down to 1min or less. This feature would be useful overall in node-gyp, but I experience it currently with nodejs-mobile-gyp.