Updated to initialize the step counter when the first `step` call occurs for each test.
Updated to initialize the step counter when the first `step` call occurs for each test.

This means that it no longer relies on the `QUnit.testStart` logging callback, nor any
global or module-level `beforeEach` hook.

Closes #4

JamesMGreene/qunit-assert-step,JamesMGreene/qunit-assert-step