libcdio_paranoia was split from libcdio in version 90, and at the same
time, the header was moved from cdio/paranoia.h to
cdio/paranoia/paranoia.h.  We can easily detect this version at
compile time which is faster than configure time.

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

Required according to RFC 3986:

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

Closes #330

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.

InputStream::Read() and InputStream::Seek() are called with the mutex
locked.  That means the implementation must not block, or unlock the
mutex before calling into blocking code.

Previously, a slow CD drive could stall the whole MPD process,
including the main thread, due to this problem.

Closes #149

This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.

Eliminate dependency on io_thread_get().

The old struct config_param remains only for top-level string options.