The `bool` return value isn't used anymore, so we can just return the
parsed object instead of passing it as an output parameter.

So long, autotools!  This is my last MPD related project to migrate
away from it.  It has its strengths, but also very obvious weaknesses
and weirdnesses.  Today, many of its quirks are not needed anymore,
and are cumbersome and slow.  Now welcome our new Meson overlords!

The number of MPD installs on Android < 5.0 is negligible, and that
API version introduces lots of useful features for MPD.

Required according to RFC 3986:

> An implementation should accept uppercase letters as equivalent to
> lowercase in scheme names

Closes #330

This way, IsFileNotFound() can detect status 404.

See commit be137a19

For remote files (not streams), this downloads as quickly as possible
to a large buffer instead of throttling the stream during playback.
Throttling can make the server impatient and it may then disconnect.

This is what Qobuz and Tidal do, and this commit attempts to solve
this by not letting the Qobuz/Tidal server wait (closes #241).

This adds a bit of overhead, but also adds flexibility to the API,
because arbitrary triggers may be invoked from that virtual method
implementation, not just Cond::signal().

The motivation for this is to make the handlers more dynamic, for the
upcoming buffering class utilizing ProxyInputStream.

This is not a plugin.

Fixes crash due to "pure virtual method called" in the "mms" input
plugin.  Closes #253

Requires Android API 21, but we want to support older versions as
well.

This change was missing in 47fa8c4c

The CurlRequest constructor can throw exceptions, therefore we must
not use "noexcept".

Allows catchers to inspect the HTTP status.