WIP: Client schemas

[SomeoneWeird]

This PR will (eventually) allow clients to pull, and cache remote method schemas, so data can be locally validated before being sent to the server.

[joshgillies]

So nice! Will see if I can make the time to offer a hand with this. 👍

[SomeoneWeird]

ref: #22

So, for this I’m thinking client.fetchSchemas(true/false)
and either: when you call a new method, it goes off and asynchronously fetches the schema for that
or: we add an endpoint that lets you request all remote methods for a service, then fetch all the schemas up front.

[SomeoneWeird]

Alright, I think this is nearly done.

Couple more changes needed (actually making it validate against the local schemas before it attempts a req)

Client.requestSchemas() can take an optional object, which allows you to map custom schema types against remote services.

If your remote service s1 is using JSON schema (using ht-tv4) and s2 is using Joi, you can do something like:

client.requestSchemas({
  s1: httv4,
  s2: htjoi
});

So the local service knows how to generate the 'stringified' schemas back into functions it can use to validate.