Support more flexible wait_for searching
This introduces backwards-incompatible (i.e., breaking) changes, so will bump our version to 3.0.0.
The existing xpath-with-substring-only means of searching documents is limiting and requires us to depend on specific text being displayed, instead of encouraging sensible class or id names for elements that can be searched independently of the presentation copy.
V3.0 will afford more flexibility to callers, allowing for better, more intuitive testing.