Add functions exposing constants for all operation/primitive pairs

Wrappers for other languages can't access constants defined by C
preprocessor macros, so they must be exposed as functions. This was
already done for the "default" implementation of each operation, but
this commit adds functions for (almost) all of the underlying
primitives.

A few are currently excluded due to problems with the automated script
used to generated this commit. They are:

  * crypto_onetimeauth_poly1305
  * crypto_generichash_blake2b
  * crypto_verify16
  * crypto_verify32