Websocket: enable 'on_open' callback after handshake

This patch enable the 'on_open' callback that aims to be triggered
after the handshake process.

Signed-off-by: Eduardo Silva <edsiper@gmail.com>
Global: fix scope and declaration of init() method

Signed-off-by: Eduardo Silva <edsiper@gmail.com>
Sessions: force init() method for initialization

Signed-off-by: Eduardo Silva <edsiper@gmail.com>
SHA256: new package for SHA256 hashing support

Signed-off-by: Eduardo Silva <edsiper@gmail.com>
Event: API modified to handle events callbacks with data argument instead of dr

Signed-off-by: Eduardo Silva <edsiper@gmail.com>
KV: Add Key-Value store engine

This package adds support for a Key-Value store engine into the stack,
the KV engine is based on Unqlite project and wraps the API callbacks.

Signed-off-by: Eduardo Silva <edsiper@gmail.com>