[release] Prepare for next development iteration

Change-Id: If737574be6565384b014b7dfc6e7966748605aab
Improved code files hierarchy

Change-Id: I879f16a9be8772bc082b8183badd61156029ea11
Isolation of JsonRPC format and auto-clean old responses

Change-Id: I8d5e1086fd9a4d011781807e74693ea9bbeeabbb
Support for requests timeouts & cancelation, and improved tests

Change-Id: I1da175a88fc69cb6ac1c03b583163f16929a9936
Packer object is now required

Change-Id: I4050ba36dd9a9fc806d56fc74b7cc7cb17f287c3
Allow responses to be request themselves

This allow to have protocols where the response messages are build
using own methods, for example an 'error' one, while still these RPC
requests being managed transparently by the library.

Request.cancel() -> RpcBuilder.cancel(request)

This allow to fix bug https://github.com/joyent/node/issues/7504
on Node.js.

Change-Id: Ic31821739791ffc112f956ba4457ad219618cd43
Fixed double-freed of requests map, and memory leak of message2key

Change-Id: I602fe93f88b8399156f3e9eb7f38486e6752e4b7
[release] Prepare release 4.2.3

Change-Id: I8db90ef7d0dde274da036eced65885dbff3589ec