Change all time conversions.  Yech.  New timer units in microseconds breaks all existing logic that used milliseconds in the conversions.  Something likely got broken doing this, probably because I confused a MSEC2TICK conversion with a TICK2MSEC conversion.  Also, the tickless OS no appears fully functional and passes the OS test on the simulator with no errors

Fix compler error in tickless code when round robin scheduling is enabled.  Other cosmetic fixes to comments

Change CONFIG_MSEC_PER_TICK to CONFIG_USEC_PER_TICK.  This gives more options for system timers in general, but more importantly, let's us realize higher resolution for the case of CONFIG_SCHED_TICKLESS=y -- of course, at the risk of some new interger overvflow problems

Add a new option CONFIG_SCHED_TICKLESS to enable the tickless OS.  This is a work in progress but should be relatively safe since the new features are only enabled by this option (Safer but not 100% safe since it does not protect from typos and other dumb errors).

Rename up_timerinit() to up_timer_initailize(); Add prototypes for candidate interfaces for the tickless OS; Don't build existing timer initialization logic if CONFIG_SCHED_TICKLESS is defined.

NSH networking: There is now a configuration option that will bring up the network on an separate thread.  Since the network bring-up is asynchronous, there are not serial console start-up delays due to the network negotiation time.

PCM decoder: Handle errors in the PCM WAV file in a way that the Nxplayer can recover gracefully: Send and Audio Complete message.

WM8904: Add reset logic to put the part back in its initial state after playing each WAV file.  Base samles per second on frame length, not bits-per-sample.  Use a different frame length for 8-bit and 16-bit data

WM8904: Correct calculation of bitrate (I am not sure why this is correct). LR clock divisor is now a constant 32-bits per frame. Conditioned out interrupt logic; it is not being used. Also added some FLL lock interrupt/poll logic (which was subsequently disabled).

WM8904 interface enable method now returns the previous interrupt state.  Correct ordering of some WM8904: Need to provide MCLK before initializing the WM8904, not after