Add test group example

Created by: lwm

Closes #20 (closed).

Added a test group in tasty-discover-example/test/FooTest.hs.

tasty-discover picks it up and reports it correctly. Resulting report looks like:

tasty-discover
  nineIsNine:                         OK
    +++ OK, passed 100 tests.
  theAnswer:                          OK
  theNumberOfTheBeast:                OK
  allMyTestsGrouped
    Testing the meaning of life.:     OK
    Testing the number of the beast.: OK
  twoIsTwo:                           OK
    +++ OK, passed 100 tests.