Explicit support for semantic versioning pre-releases.

[jmalloc]

Hi all,

I am wondering if explicit support for semantic versioning would be a desirable and reasonable addition to this action?

What I am proposing is allowing semver as valid value for the prerelease field in the action configuration. Use of this value would mark a release as a "full-release" (i.e., non-pre-release) only if:

• the tag name is valid semantic version, optionally prefixed with a v
• the major version is greater than zero
• the version does not contain a pre-release component

If such a feature is welcome I'll attempt to submit a PR :)

/cc @ezzatron