This commit changes synchronous decoding so that the calling thread is
the one which performs the decoding. Previously, decoding was done on
the job threads which was then waited on by an event on the calling
thread. The rationale for this design was to keep decoding on a single
code path, however this creates a problem for programs that would
prefer not to have any asynchronous job threads. In this case, these
synchronously decoded sounds would never get decoded because there
would not be any threads available to actually perform the decoding.

This commit enables the resource manager to be able to be used without
a job thread so long as asynchronous decoding and streaming are not
used. This scenario could be useful for programs that want to pre-load
all of their sounds at load time and save some system resources by not
incurring the overhead of an additional unnecessary thread.

This new system is used for asynchronous decoding of sound data. The
main improvement with this one over the old one is the ability to do
multi-producer, multi-consumer lock-free posting of messages which
means multiple threads can be used to process jobs simultaneously
rather than a single thread processing all jobs serially.

Decoding is inherently serial which means multiple job threads is only
useful when decoding multiple sounds. Each individual sound will be
decoded serially.

Another change with this commit is the ability for applications to
control whether or not the resource manager manages it's own job
threads. This is useful if an application wants to manage the job queue
themselves if, for example, they want to integrate it more closely with
their existing job system.