Despite the name “package-version-parser,” PVP didn’t really provide a way to parse a package version. With this change, if you want to get the minor version of “1.2.3_4”, for example, you can just write `PV.parse(“1.2.3_4”).minor`. This simplifies the internals of PVP as well.
When you parse a version, you now get an instance of PackageVersion with a documented set of fields.
Also, make PVP work on the client. When called directly from the tool, semver is loaded the same way as before. When PVP is used as a package, it uses a copy of semver v4.1.0 kept inside the package.
This change is intended to be 100% behavior-preserving.
