Implement string variable interpolater

This adds a `StringSub` struct which inserts variable mappings into a
format string and updates download targets' URLs to use it.

Change-Id: Ifc0064415a2e541efbeb349006824001dd54158b
Commit-Queue: Alexei Frolov <>
Reviewed-by: Erik Gilling <>
5 files changed
tree: c2e620a27037cb858a472cab8f999a6927109d5a
  1. examples/
  2. qg/
  3. qg-cli/
  4. tools/
  5. .gitignore
  6. Cargo.toml
  7. rustfmt.toml