the code here tried to guard DSD features behind ENABLE_DSD. However, the sample rate setting should be shared between two scenarios. 

https://github.com/MusicPlayerDaemon/MPD/commit/40a1ebee295c569521ea17ffdedc641d1aedd9cb#diff-ce7ecec9ea9ca3df90d9c290cb3ef9d4R795


The code runs fine if the dac supports the sample rate, as Mac OS  will use the device rate if stream rate is 0. 
However, when DAC is uncapable of processing the sample rate, a wrong rate (device rate) will be used for the stream rate.

Add link to more recent libsidplayfp and correct URL pointing to libsidplay2.

Prepare to allow more complex expressions.

Required for "modified-since".

All DetachedSong instances should be converted to LightSong first,
which is a very cheap operation.

This is kind of a revert of commit
b2e3c075, which is not any longer
necessary since commit 0dd4b52b
removed the last call to `av_open_input_stream()`.

Instead of copying the offset from our `input`, copy the requested
offset to our `offset` attribute.

By the time Seek() finishes, our input's offset may have advanced
already, having read some more data, thus giving us a bogus offset.

This fixes spurious decoder failues (closes #320).

Closes #89

Will allow more complex fitler expression, such as negation (#89).

Was converted to reStructuredText / Sphinx in commit
8a689e68

Not yet wired to the protocol.