Respect semantic versioning

See <http://semver.org/>.

For now, this just boils down to naming the version `v1.0.0` instead of `v1.0`.

Following semver is a no-brainer that has many benefits, among which the possibility to create a [Homebrew](https://github.com/Homebrew/homebrew) formula for installing HashPump and get it accepted into the main repository.