Provide more command-line options

[propensive]

Probably's command-line interface accepts a list of arguments, being the hashes of the tests it should run. (If none are specified, then all tests are run.)

But it would be useful to have options which help to format the report that is printed after the tests are run. For example, to show or hide the test times, or to print full stack traces when exceptions are thrown.

We need to parse the arguments (which should be in -f/--foo style), and then change the output format according to the choices.

Some suggestions for flags:

• -S/--no-suites: do not run sub-suites
• -q/--quiet do not print any output (just return success or failure exit status)
• -T/--no-times do not display test timing columns
• -e/--exceptions print full stack traces