JSON-RPC v6.0.0

Major overhaul of the library and consolidation to single repository.

1. We switched to futures which simplified a lot of code in core.
2. Serde dependency updated to 0.9
3. IoHandler now supports Middleware and Metadata (both opt-in, second being a slight deviation from json-rpc standard)
4. jsonrpc-macros library simplifying implementation of complex services.

See examples for each crate for more details.

Published crates:

jsonrpc-core = "6.0"
jsonrpc-macros = "6.0"
jsonrpc-ipc-server = "6.0"
jsonrpc-tcp-server = "6.0"

jsonrpc-http-server uses unstable asynchronous hyper, so it needs to be referenced directly from github:

jsonrpc-http-server = { git = "http://github.com/ethcore/jsonrpc", tag = "v6.0.0" }