RUN-BANG-COMMAND runs even from other packages.

This commit also ditches some dead code and updates the README.
PRACTICE loop can now terminate.
The assert in PRACTICE no longer reflects an invariant.
Adds placeholder bogo-config.
Updates COMMAND-LIST; fixes wording in LENGTH bang command.
Deletes a dead function.
Adds practice hooks.

There's also practice list management in config.lisp that
uses the hooks by way of example.
Bugfixes.

Supersede replaces a file; overwrite may leave old garbage.
Adding strings to the error list should avoid dupes.
The table hooks take arguments, which are now reflected in their definitions.
Removes dead var from PRACTICE.