Fix for recent instability in building

Added

• Improved ability to embed pFUnit in the source tree of other projects.

Changed

• pFUnit now uses CMake namespaces. Upstream projects should now link
  against PFUNIT::funit (or PFUNIT::pfunit) rather than just funit. Users that
  build test suites using the add_pfunit_ctest() macro should not see an impact.

Fixed

• The add_pfunit_ctest() macro could fail under several not-so-rare
  circumstances. One way is for CMake to fail to build
  OTHER_SOURCES before the driver as it cannot correctly analyze
  the indirect Fortran USE PFUNIT_EXTRA_INITIALIZE statement. The
  other is when using paralle builds with multiple test suites using
  Intel and the -save-temps flag. Here the compiler would overwrite the
  driver.i90 in the build directory and produce confusing results.

  The solution is to use Cmake configure_file() to preprocess the driver
  directly on a per-suite basis. This will allow CMake+FPP to corretly
  analyze dependencies and avoid reuse of driver.i90.