* Bump NQPTP_SHM_STRUCTURES_VERSION to 8.

* Bump NQPTP_SHM_STRUCTURES_VERSION to 8.
* Remove the ability to handle multiple instances of AirPlay-2-capable Shairport Sync on the same system -- it seems clear that clients can not use this facility.
* Greatly simplify NQPTP by only monitoring PTP information coming from the client, ignoring all other PTP information.
* Improve the accuracy of the clock by taking correction field information into account.
* In addition to trying to restart a clock that is silent, also send a restart to a clock if the clock's grandmaster appears to have stopped.

Squashed commit of the following:
    Add some experimental exploratory code.
    Ignore the INSTALL document. Let INSTALL always be autogenerated.
    Enhanced and corrected ptp defiinitions.
    Fix shm name to work with FreeBSD. Update the SHM version.
    Change order of includes to avoid a compilation error in FreeBSD
    Fix potential bugs in finding a clock ID in a FreeBSD device.
    Only try to restart a stopped clock if it's the clock itself that has stopped and not a different grandmaster. Allow fast changes for up to one second after the start of mastership.