v0.2.0

This is the second official release of alsa-gobject project.

 * https://github.com/alsa-project/alsa-gobject/releases/tag/v0.2.0

It includes some enhancements and bug fixes.

* Some implementations of GLib GQuark is exported as error domain and
  corresponding enumerations are added. This improves error reporting
  in each libraries. It closes issue #47[2].
* Selection of substream in ALSARawmidi.StreamPair.open() now works well.
  This closes issue #53[3].
* Prototypes of some methods in ALSACtl.Card object for data of
  TLV(Type-Length-Value) in ALSA control interface are changed without
  backward compatibility. Corresponding exported symbols are maintained
  by new symbol version. In detail, refer to #55[4].
* Error handling is changed so that function call with invalid argument
  just returns with warnings instead of generating GError, according to
  convention for GLib application. Memory allocation failure is supposed
  to be unrecoverable error and aborts program, as well.
* It's possible to build for older version Linux kernel, therefore
  build dependency is now Linux kernel v4.5 or later.

For the new release, documentations are also updated. They're
auto-generated by gtk-doc[5] from function annotations:

 * https://alsa-project.github.io/alsa-gobject-docs/

The new release of Rust crates are available as well in repository.
They're auto-generated by gtk-rs/gir[6]:

 * https://github.com/alsa-project/alsa-gobject-rs/

[1] https://github.com/alsa-project/alsa-gobject
[2] https://github.com/alsa-project/alsa-gobject/issues/47
[3] https://github.com/alsa-project/alsa-gobject/issues/53
[4] https://github.com/alsa-project/alsa-gobject/pull/55
[5] https://developer.gnome.org/gtk-doc-manual/
[6] https://github.com/gtk-rs/gir

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>