Draft: Adding tooling for repo and pool management

This will fix #14 (closed) and add tooling for basic file management of packages. The following should be True now:

1. Pre-commit file actions:
   • Add packages to pool dir via copy + rename
     • File already exists with different content → error
2. Post-commit file actions:
   • Add symlinks to repo dir
   • Generate new DBs
   • Rename new DBs over current DBs
3. Garbage-collect files:
   • Remove unused symlinks from repo dir
   • Remove unused packages from pool dir

Usage

Pool

Adding a file to pool

$ pool_update --package ~/gcc-11.2.0-4-x86_64.pkg.tar.zst --add

Removing a file from pool

$ pool_update --package gcc-11.2.0-4-x86_64.pkg.tar.zst --remove

Repo

Adding a file to repo

$ repo_update --package gcc-11.2.0-4-x86_64.pkg.tar.zst --add

Removing a file from repo

$ repo_update --package gcc-11.2.0-4-x86_64.pkg.tar.zst --remove