Yamlns

- pytest utils:
- `text_snapshot`: a pytest fixture that compares a text with the previous validated execution
- `yaml_snapshot`: a pytest fixture that compares the yaml dump of the value with the previous validated execution
- `assert_ns_equal`: a custom assertion equivalent to `assertNsEqual` for `unittest`
- `ns` alias for `namespace`

- github actions for ci and release
- improved test coverage

- py2 compatible loading

- Dump multiline strings verbatim (|) instead of quoted whenever possible
- Py3: removed 0 padded numbers in date tests
- Improved coverage in templating code
- Fix: removed a spurious trace

- Fix: datetimes were loaded as dates. Closes 2

- Fix: working on Py2 installs without Pathlib2