Enable running a concrete test from a test file

[Chemaclass]

Currently

Right now, you can specify what functions to run with -f|--filter option

 ./bashunit tests/unit/test_doubles_test.sh --filter test_spy_with_pipe_in_arguments

Task

Enable running a concrete test from a test file using :: syntax

For example:

./bashunit tests/unit/test_doubles_test.sh::test_spy_with_pipe_in_arguments

As another idea, by line number

./bashunit tests/unit/test_doubles_test.sh:171