This type defines acceptable formats for the version of a
module. The version may be a semantic version, or a YANG
revision statement date, and may include wildcards when
included in a bundle compatibility list, e.g.:
semver format: <major>.<minor>.<patch>
examples: 0.1.0, 2.1.0, 1.1.*, 2.*.*
revision format: YYYY-MM-DD
example: 2016-11-31