Add Timer reporter
Improve error reporting somewhat

Timeout errors are not nice, but that's what you get when the suite
runner fails with some internal exception if the tests are written
like they were.
Decorate finish messages from the suite runner with timing information
Require the default slowness threshold parameter in the Timer reporter

Otherwise it will silently not report slowness if the parameter is missing
Set a slow threshold in test.js
Report slow test times in the spec progress reporter
Fix linter issue
Merge pull request #38 from pereckerdal/measure-test-time

Measure the time for each test and report it