params: add multi-level verbosity

Now we can have --verbose=[012], so that the default (0) is still quiet,
the easy verbose flag (--verbose or -v) is noisy but useful (1), and if
you really want some extra noise, you can choose (2). Right now, there
is some minimal extra noise in (2), but this may be expanded if we want
more run-time debuggability, rather than recompiling with 'make debug'.
model: cosmetic output improvements

A few cosmetic improvements:

* Provide more uniform newlines

* Clearly show which output is produced by the test program

* Provide clear heading to show which output belongs to which program
  execution

* Label the program trace if it has bugs

I'm sure there's more that could be improved, but that's it for now.
README: updated help text