Added an option, called exit, that when set to false, will make the
tests not exit at the end. This is useful when you are doing Lisp-like
development having a REPL (interpreter/prompt) opened in Emacs and
running the tests over and over on it.
Currently, the tests will exit the interpreter, causing the in-Emacs
interpreter to close as well.
It is by default set to false, so the default behavior is still the
same. When set to true the default behavior shouldn't change much
because at the end of the tests you are going to exit anyway. The only
difference is that no exit code will be provided. There's actually
something else, because the Python test suite hangs in a test case when
this is set to true, but this should be of no concern, as default is false.