Add VP support to example.

[davidlehn]

• Adding VP support to futher expand the example.
• Using did:key for VC and did:web for VP to add variety.
• Print out logging as we go.
• Print readable first stack trace if there are verify errors.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 90.44%. Comparing base (e02e347) to head (04588c3).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## example-usage-script #184 +/- ## ===================================================== Coverage 90.44% 90.44% ===================================================== Files 5 5 Lines 1057 1057 ===================================================== Hits 956 956 Misses 101 101 ``` ------ [Continue to review full report in Codecov by Sentry](https://app.codecov.io/gh/digitalbazaar/vc/pull/184?dropdown=coverage&src=pr&el=continue&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=digitalbazaar). > **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=digitalbazaar) > `Δ = absolute (impact)`, `ø = not affected`, `? = missing data` > Powered by [Codecov](https://app.codecov.io/gh/digitalbazaar/vc/pull/184?dropdown=coverage&src=pr&el=footer&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=digitalbazaar). Last update [e02e347...04588c3](https://app.codecov.io/gh/digitalbazaar/vc/pull/184?dropdown=coverage&src=pr&el=lastupdated&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=digitalbazaar). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=digitalbazaar).