Test cleanups for style and clarity.
Test cleanups for style and clarity.

* Enhance output when expected symbols don't match.
* Adjust symbol tests for existence of BPVCS_RESET_COLOR.
* Add comments.
* Don't use both function and ()s, use just ()s.
* Clean up check() and rename it to test_prompt().
* Put vars in {}s.
* Make failure output a bit better.
* Use [[ instead of [.
* Align columns in some table-likes for better scanning.
* Factor into more functions.  Add main function.
* Make falure output more consistent.

meadowface/bash-prompt-vcs