Simplified libpsinc to remove the Acquirer class - we just
have a Camera now.

* Initialisation of cameras restructured to be ready for cameras
shipped with non-default devices or imaging chips

* Removed the Refreshed event - it's no longer needed since
registers are now always fully refreshed at connection and a full
refresh cannot be otherwise requested.

* The available devices are now created directly in code, not
parsed from baked-in xml

README is now out of date and needs a rewrite.