Add a cache system

[n-peugnet]

If I understood correctly, this plugin includes dependencies by browsing recursively every file looking for require calls.

This process takes a lot of time if the dependencies tree is big and could be made a lot faster with a cache system.

For example the npm packages dependencies never changes except when the version changes so after it has been browsed once, no need to recheck it in further deployment.

[dougmoscrop]

It only parses the AST for local files, once it finds a dependency in node_modules, it switches to just pulling in dependencies noted in package.json (too many corner cases).

Since recent npm dedupes natively, I'm not sure the advantage of a cache. I've never seen this package step take very long, but the built-in serverless one does. Make sure you set:

package:
  excludeDevDependencies: false

[n-peugnet]

Thank you it was as you said the built-in one that took a lot of time.

However I didn't find this information anywhere in your docs.

[dougmoscrop]

Thanks, good point! I added it to the README.