Add cacert option for curl plugin

    add cacert option for Curl plugin. Allows to set cacert for curl lib
    Added documentation line into doc/plugins.rst with explanation for cacert option

I havn't yet figured out how to use Android's system CA certificates
with CURL/OpenSSL, so a temporary workaround is to disable verify_peer
by default.  The data MPD transfers isn't extremely important, so the
servers's authenticity isn't extremely important either.

Found with readability-uppercase-literal-suffix
Signed-off-by: Rosen Penev <rosenp@gmail.com>

The former was deprecated with C++14.

According to the C++11 and C++17 standards, both files are identical.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Found with readability-uppercase-literal-suffix
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Found with modernize-use-override
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Like fe598e7d

Extends the URI fragment parameter added in
commit cf9ee339

Closes https://github.com/MusicPlayerDaemon/MPD/issues/679

Fix src/ls.cxx to only print unique schemas.
Refactor src/ls.cxx to use src/input/InputPlugin functionality.

Add dynamic enumeration support to curl plugin.

Let the caller decide what to do with the original exception.

Since we switched from autotools to Meson in commit
94592c14, we don't need to include
`config.h` early to properly enable large file support.  Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.

This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.

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.

See commit be137a19

Prepare to allow callers to pass custom request headers.

Allows the caller to decide whether to enable the feature.

The IcyMetaDataParser cannot be initialized already in OnHeaders(),
because it will be initialized late in that method; and there will not
be another OnHeaders() call, because streams with Icy metadata are not
seekable, thus there will not be another HTTP request.