Add support for prerelease tags Semver allows [prerelease tags][0], denoted by appending a hyphen and a series of dot-separated identifiers immediately following the patch version. Let's add support for them! Or at least partial support. This might take a couple steps. src/version.rs -------------- The allowed characters in the prerelease label are alphanumerics, hyphens, and periods. We'll call that `letters_numbers_dash_dot` and tack on an optional prerelease version in our regex. Since that line was getting a bit long, we'll add *x mode*, which allows us to describe the regex over multiple lines, with comments for each important bit. We also have to add the `pre` field to the `Version` struct and capture it from the regex. For now, we're just reading the whole string into an optional single-element vector. Later on, we will have to break it apart into individual dot-separated identifiers. [0]: http://semver.org/#spec-item-9