Add README.md and some scripts to the main branch, plus a few changes to cofact.c and Makefile.

Added README.md to the main branch.
Added link_gwnum script to create links to the gwnum library.
Added run_all script to run cofact on each Fermat number from F0 to F29 using a reasonably fast method. This can be used for regression testing when making code changes.
In cofact.c change the output message on a successful Suyama test from declaring the cofactor a prime to declaring it a probable prime (PRP). Changed the version to 0.8.2.
In Makefile removed the reference to gwnum.ld since it is no longer needed.

primesearch / cofact