Add known hexadecimal words

Summary:
The log is parsed to find hexadecimal hashes.

Some English words can be false positives, and such false positives are
ignored through an hexadecimal known words list.

Currently, the list only contains words used in the log, 'added' and 'ed25519'.

This changes adds some more, from a ^[a-f]+$ search in /usr/share/dict/words,
so the log should be safe in the future.

Test Plan: Ensure words aren't parse as SHA hashes.

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1335