pdl: Convert main from clap to argh

clap has incompatible versions on aosp-master (3.2),
tm-mainline-prod (2.2) and emu-master-dev (4.1) making
it impossible to provide a main compatible with all branches.

argh is much more stable.

Test: cargo run tests/canonical/le_test_file.pdl
Change-Id: I9ffb5119e2e1e90562411c782f5cd4ccd926b93c