Remove opcode processors from the public API

We always invoke the processor function for an opcode by calling the
process() method on an Opcode object.  That method uses the name of
the opcode to find the processor in a look-up table.  This patch makes
that table private because the process() method is all we need, not
access to the processor functions themselves.
Makefile: Update ‘make tags’ to find opcode processors

This change is necessary because we have changed the name of the table
that contained opcode processor functions.
Merge branch 'hide-opcode-processors'

* hide-opcode-processors:
  Makefile: Update ‘make tags’ to find opcode processors
  Remove opcode processors from the public API