Add input wordlist functionality

[denandz]

This pull request adds the ability to pass pencode an input wordlist, rather than only accepting input via stdin.

The use case here is when fuzzing something like a JSON or SOAP API with predefined wordlists and ffuf/intruder/whatever. I'd like to be able to pass my attack wordlist to pencode directly, and have it spit out the encoded/escaped versions of the payloads that I can subsequently use to fuzz a specific target without unintentionally breaking the JSON/XML encoder.