Sample-tester

Setup failures preempt test cases; doc fixes; tag interpolation in log statements. gen-manifest: quote YAML values, default to schema v3

This release adds support for implicit tags, which are tags not defined explicitly in the manifest docs but which are applied automatically to all elements in a given manifest doc.

This release defines two such implicit tags, `manifest_source` (the full path to the source manifest file, including the filename itself), and `manifest_dir` (the directory of the source manifest file).

More details in 76

* Change `*not_contains*` directives to be `*_exclude_*` directives (66)
* Support manifest schema v3 (67)
* gen-manifest tool:
* make into a separate executable in the PyPI package (69)
* allow generating manifest schema v3 files and passing arbitrary key/value pairs (74)

This contains a tool, grafted onto the sample tester in a not-too-clean way, to generate manifest files from scratch. Submitting/releasing this to unblock sample generation.

Provide `assert_contains_any`, `assert_not_contains_some` to match at least one string from a list

Case-insensitive `*_contains`, tweaks to `env` fields