Eliminates a number of allocations, because callers don't need to copy
the strings to a newly allocated buffer only to null-terminate them.
And most callers don't need to have a null-terminated string.

No variable-length arrays on the stack.

Variable-length arrays are a C-only feature.

release v0.21.10

Since we now don't duplicate all items, we can easily remove the 64kB
limit from OpusReader::ReadString() and instead silently ignore and
skip all strings which are longer than 4 kB.

This fixes a tag duplication bug with Opus file containing a very long
`METADATA_BLOCK_PICTURE` tag, which occurred because the Opus plugin
returned false after parsing all tags, and then the MPD core fell back
to FFmpeg which scanned the tags again.

Return `404 not found` for some common well-known paths, as clients requesting them usually do that automatically and don't expect endless audio stram.

Closes #572

memcmp use may result in out of bounds access

Fixes the Windows build.

Let the caller do this.  Our GetSuffix() function was broken anyway.

Don't call Seek() if the stream is already at the beginning.  This
avoids unnecessary exceptions if seeking is not implemented by an
Inputstream implementation.

This reverts commit ff3e2c05.  The
check was necessary, after all, because this is what checked whether
the decoder had finished the current or the next song.

> The "queued" flag can only possibly be set if the decoder is still
> decoding the current song or if the decoder is stopped.

That was wrong because ProcessCommand() sets `queued=true` and also
starts the decoder (if it was idle).

> This is also what the following assert() checks.

That was also wrong, because the assert() has two conditions.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/566

Closes https://github.com/MusicPlayerDaemon/MPD/issues/568

According to http://www.sphinx-doc.org/en/master/usage/restructuredtext/basics.html#sections