rtx install [email protected]~1

[jdx]

I want to add a "~N" syntax to version numbers which would map to the version number minus N. This can be useful for declaring "I want the latest version and the second latest version".

It may be possible for a plugin to have a tilde in it as a valid version though, so this may require a bit of care to not do this modification if there is a version that matches exactly.

Related to #21 and #49