Support compound expressions

[ysbaddaden]

We should add support for compound expressions in version requirements, that is the ability to specify multiple version requirements A valid use case is to require a minimum version while still allowing an approximate version on a higher segment. For example:

• ~> 1.0.0, >= 1.2.3.rc for example.

Maybe we could also add support for the semver caret expression. It can be expressed with a compound expression, but maybe it's nice to have. I don't know, I never use it. For example:

• ^ 1.2.3 translated as ~> 1.0, >= 1.2.3.