New :command-verbosity option.

You can set a command's verbosity with (e.g.):

  (set-option :command-verbosity (get-model 0))

which will mute get-model except for its normal model output.

You can also set a default for all supported commands:

  (set-option :command-verbosity (* 1))

Legal verbosity levels are:

0 - never print error or "success" responses, but print normal output
1 - print error messages and normal output, but not "success" messages
2 - print everything (success and error messages, and normal output)

The default verbosity level for all commands is 2; however, see below
about :print-success.

Note that set-option itself is affected, which can lead to the
suppression of errors.  For example, if you invoke:

  (set-option :command-verbosity (* 0))
  (set-option :command-verbosity (* 3))

then the second command fails (since "3" is an illegal verbosity level)
but the error is silenced.  So please use :command-verbosity with care.

You can also get the verbosity list with

  (get-option :command-verbosity)

Finally, note that in keeping with the SMT-LIB standard, the :print-success
option is a "master switch" for "success" responses.  So even if a command
has verbosity level 2, you won't see "success" responses unless
:print-success is *also* on.