Split node-vault in different npm packages

[kr1sp1n]

My idea is to split this library in different npm packages because the functionality of vault is growing so fast. We could have a basic client for system backend and then extended clients for secret backends, auth backends and plugin backends as well. I would love to keep the repo and manage the publishing of the npm packages with a tool like lerna (https://github.com/lerna/lerna). WDYT?

[DaniGuardiola]

@kr1sp1n I would close this because of the reasons I wrote in this issue comment

[DaniGuardiola]

Closing because of the reasons mentioned here