Crash during argument parsing

[R1kM]

Running Charon on crate lazy-static.rs leads to a panic with error message

thread 'main' panicked at src/bin/charon-driver/driver.rs:170:5:
assertion failed: indices.len() <= 1

One hypothesis raised by @Nadrieril is that this is due to the crate name ending in .rs, that should be better handled during argument parsing.