This allows virtualenv-multiver to accept version ranges, instead of

having to list out every single version. For example, 2.7 3.8-3.11

will expand to 2.7 3.8 3.9 3.10 3.11.
This reduces errors and greatly simplifies usage.
Duplicate verisons are also now removed, preventing any redundant

environment creation.

Used this to create many environments.
Tested that versions are correctly deduplicated.