clean up type declarations in primes functions
Clean up NTH-DIGIT, and make negative numbers more sensible.

Thanks to stassats.
Make SUBDIVIDE better.

Thanks to stassats.
Fix PARTITION-IF.

Thanks to stassats.
Clean up SLICE and N-GRAMS.
Simplify NCYCLE.

Thanks to stassats.
Improve SAFE-NTH.

Thanks to stassats.
Make LIST-TO-VECTOR and SEQUENCE-TO-LIST use COERCE, and check their
type.
improve IMPLODE and EXPLODE.
Improve TAILS.

Thanks to stassats.
Improve EQUIVALENCE-CLASSES. Uses lists now.
Improve SAME-NAME and ENSURE-KEYWORD.

Thanks to stassats.
Add NIL-block and tagbody to DOSEQ.
Rewrite RERANK-ARRAY to not use displaced arrays.