http adapter: pre/postProcess, fix destroy and all

preProcess() ensures that null fields are excluded from the wire. I've experienced jQuery/node/express 3.0 turning nulls into empty strings.

postProcess() ensures that Date fields are actually turned back into dates. JSON, you're annoying sometimes.

destroy() is now implemented.

all() now URL encodes any query filters provided.
Merge pull request #218 from NiKnight/http

http adapter: pre/postProcess, fix destroy and all