add semantic versioning (semver.org) validator

[thiagowfx]

https://semver.org/#is-there-a-suggested-regular-expression-regex-to-check-a-semver-string

[thiagowfx]

If you deem this PR worthwhile, please accept the workflow so that we can verify whether the tests pass.

[cblakkan]

Looks like you've got a typo in the test

      def test_semver():
          """
          - https://semver.org/#is-there-a-suggested-regular-expression-regex-to-check-a-semver-string
          - https://regex101.com/r/Ly7O1x/3/
          """
  >       v = val.Semver()
  E       AttributeError: module 'yamale.validators' has no attribute 'Semver'. Did you mean: 'SemVer'?

[thiagowfx]

Ooops! Fixed