The new sip build system complies with pep 517 and
requires configuration by a standard pyproject.toml
file rather than running a single command. Along with
these changes the fixed sip.h file has been removed in
favour of a header generated locally if required.

We now support both the sip build systems as this is
required in our current support for multiple OSes. In
the process of adding support some cleanup has been
included:
  - the .sip files in our tree are now full module defs
    rather than the boilerplate being filled in by CMake,
    giving each module more flexibility.
  - the sipwrapper file has been removed in favour of a
    simpler script to simply strip the problematic code
    for C++17 compatability.