gtk3: implement Gtk::SearchBar
glib2: reduce locking on object conversion
gtk3 sample: remove needless version check
gtk3 sample: use " (double quote) for string literal
gtk3 sample: suppress warnings for deprecated API
gtk3 sample: remove trailing spaces
gtk3 sample: use " (double quote) for string literal
gtk3 sample: suppress warnings for deprecated API
gtk3 sample: fold a long line
gtk3 sample: add missing shebang

TODO: give other files execute permission and shebang.
gi: add EnumInfo#error_domain
glib2: fix type
glib2: use GObject for GType
glib2: export rbg_inspect() for convenience
gi: support defining error
glib2: remove trailing spaces
glib2: use module for common methods
glib2: create code level error classes and use them rather than domain error
gio2: support error
gi: improve guessing target constructor