Support more ways of specifying the installation version

[ItsDrike]

Currently, the way script handles versioning is simply by passing the version over to pip as poetry=={version}. This is fine, however it would be nice if we could set the version to something like ^1.3.0, or similar.

This probably shouldn't be too hard to handle, as there's already a regex checking for semver compatibility, and these are just some set of additional characters that could optionally be there. If this specifier isn't there, the script can just use the current approach of ==.

[MatthijsBurgh]

Or just 1.8, where is would select the most recent version of 1.8.X. This would be really helpful.