Exports in package.json seem too restricted

[ehg-fblenkle]

Hey,

I need to develop my own handler against redis (for reasons, see #169). But it's very hard, because I cannot import the types/utils I need. At first I thought it would be sufficient to "grant access" to types of cache-handler-types.d.ts, but as I developed against a "patched version" I realized I also need some utils (e.g. convertStringsToBuffers).

I'm not used to have these issues when dealing with other packages, so I wanted to ask if there is a reason for these strict exports.