Add simple subcommand argument parsing structure

This pulls in clap and sets up a registry of subcommands, providing an
example "hello" subcommand.

Change-Id: Ie326ec455fc75ba0509558faac8f7b771f81478a
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/qg/+/119539
Reviewed-by: Erik Gilling <konkers@google.com>
Commit-Queue: Alexei Frolov <frolv@google.com>
5 files changed
tree: 777956a3623f9479c8eb12c4f4a509ac92513baa
  1. qg/
  2. qg-cli/
  3. tools/
  4. .gitignore
  5. Cargo.lock
  6. Cargo.toml
  7. rustfmt.toml