request pooling

[gr2m]

follow up for hoodiehq/hoodie#118

Basic idea is to pool GET request, e.g. when executing hoodie.request('/hoodie/api') in quick succession it will not send multiple requests, but only send one request and return the promise for the others.

Let’s debate if this is still something we want. I’m not sure if this is still an issue with the new Hoodie at all, probably not