Use the output from git describe as deb package version

[NickVolynkin]

Currently, deb packages always have the hardcoded version 0.1.0. It results in a few problems:

• It's not possible to choose versions when installing from a repository. We can only hope that we're installing the latest version.
• It's hard to trace the installed version to the commit of nilfoundation/zkllvm that the package was built from.

Packages should have versions, based on tags and produced with git describe --tags HEAD. For example:

• aea5b96 — v0.0.70
• a0ca4f9 — v0.0.70-5-ga0ca4f9

v0.0.70-5-ga0ca4f9 has the following meaning:

• Latest tagged commit was v0.0.70.
• Current commit is 5th since the tag.
• And it's hash is a0ca4f9 (also note the letter g before the hash).

[NickVolynkin]

Apparently, I was wrong about the package versions. They do use the tag's version. However, there's a 0.1.0 package in the repository, and it overshadows newer packages.

From the upload log:

 Updating deb repository: deb.nil.foundation/ubuntu/
Skipping: 'pool/focal/main/z/zkllvm/zkllvm-stdlib_0.0-1_all.deb'
Skipping: 'pool/focal/main/z/zkllvm/zkllvm_0.0.63-1_amd64.deb'
Updating: 'pool/main/z/zkllvm/zkllvm-stdlib_0.0-1_all.deb'
Skipping: 'pool/main/z/zkllvm/zkllvm_0.0.0-45_amd64.deb'
Skipping: 'pool/main/z/zkllvm/zkllvm_0.0.58_amd64.deb'
Skipping: 'pool/main/z/zkllvm/zkllvm_0.0.68_amd64.deb'
Adding: 'pool/main/z/zkllvm/zkllvm_0.0.71_amd64.deb'
Skipping: 'pool/main/z/zkllvm/zkllvm_0.1.0_amd64.deb'