Prepare for integration with main Starlink build

- dat_par.h is now static
- Library change to libhds_v5 to match v4 scheme
- Now build with _v5 API symbols by default
We are resetting the version number to hdf-v5 version 1
Add version int to HDSLoc

This allows a future HDS wrapper library to be able to quickly
work out which version to use for a given locator.