Deprecate my "exc" repo

[grencez]

• Add readme with links to new things at grencez.dev. Updating this is also part of future steps.
• 82000 code
• 82000 mpi code??
• bddtest code (maybe)
• count-search code
• fliptil code
• leadercard code
• pazucarlo code
• polystep code with article
• soniagen code (don't migrate, just mark broken)
• urandom code
• polystep article with code
• graph isomorphism article
• valuations article
• Archive it.