Automatically install vyper version specified in version pragma

[spinoch]

As a user, I want blackadder to automatically fetch and install the vyper version specified in my vyper file so that it can format the file.

Brownie implements this functionality here https://github.com/eth-brownie/brownie/blob/a88888a8724c0e99085502b7ae8ded835a2b0934/brownie/project/compiler/vyper.py

[spinoch]

This is causing the red builds at the moment

[iamdefinitelyahuman]

Brownie accomplishes this via a package called vvm - https://github.com/vyperlang/vvm

[spinoch]

Kind of blocked by vyperlang/vvm#5 atm

[spinoch]

Created this without thinking about the issue too much: it makes more sense if we make blackadder parse the AST even if the vyper version installed is different than the version specified in pragma (at least, if the major version is the same). Will phrase this in another issue

[spinoch]

@iamdefinitelyahuman what would you think about isolating the logic of brownie's brownie.compiler.vyper.find.*vyper_version?
I think it makes sense to use that same logic in blackadder, but I don't think it makes sense to have brownie as a dependency.
Maybe putting it in vvm.utils could work for both brownie and blackadder

[iamdefinitelyahuman]

I think it could live in vvm.utils without hurting anybody too much :)