Structured Logging

[jf2048]

Adds bindings for these functions:

• glib::log_set_writer_func
• glib::log_structured_array
  • Requires a new GStr wrapper for a borrowed GString, so we can avoid copying the log keys.
• glib::log_variant
• glib::log_writer_default
• glib::log_writer_format_fields
• glib::log_writer_journald
• glib::log_writer_standard_streams
• glib::log_writer_is_journald - unix only
• glib::log_writer_supports_color - unix only
• glib::log_writer_default_set_use_stderr
• glib::log_writer_default_would_drop

And some new macros:

• glib::gstr - Turns a string literal into a &'static GStr, by appending a nul byte at compile time
• glib::log_structured - The main interface. From the docs:

log_structured!(
    "test",
    LogLevel::Debug,
    {
        // a normal string field
        "MY_FIELD" => "123";
        // fields can also take format arguments
        "MY_FIELD2" => "abc {}", "def";
        // single argument can be a &str or a &[u8] or anything else satsfying AsRef<[u8]>
        "MY_FIELD3" => CString::new("my string").unwrap().to_bytes();
        // field names can also be dynamic, taking an AsRef<GStr>
        GString::from("MY_FIELD4") => b"a binary string".to_owned();
        // the main log message goes in the MESSAGE field
        "MESSAGE" => "test: {} {}", 1, 2, ;
    }
);

[sdroege]

Looks nice otherwise