hinawa-rs v0.2.0 release

This release includes optimization for libhinawa v2.1.0 release, which includes
public error quark, error codes, and signaling-driven asynchronous APIs for transactions.

For error reporting, below structures and traits are newly introduced:

* hinawa::FwNodeError
* hinawa::FwReqError
* hinawa::FwFcpError
* hinawa::SndUnitError
* hinawa::SndDiceError
* hinawa::SndEfwError

For implementation of GObject signal, below functions are newly available:

* hinawa::FwReq.connect_responded()
* hinawa::SndEfw.connect_responded()
* hinawa::FwFcp.connect_responded()

For signaling-driven asynchronous API, below functions are newly available:

* hinawa::FwReq.transaction_async()
* hinawa::SndEfw.transaction_async()
* hinawa::FwFcp.command()

For synchronous API utilizing the above signals and functions, below
functions are newly available:

* hinawa::FwReq.transaction_sync
* hinawa::SndEfw.transaction_sync
* hinawa::FwFcp.avc_transaction