Summary:
Fixes T11586. First pass at a class for displaying invisible characters. Still need to:
- Write a couple unit tests
- Add some styling to the .invisible-special spans
- Actually start using the class when displaying form errors to users
Currently this makes the string `"\nab\x00c\x01d\te\nf"` look like:
{F1812711}
Test Plan:
Unit tests all pass and run in <1ms:
{F1812998}
Reviewers: epriestley, #blessed_reviewers, chad
Reviewed By: epriestley, #blessed_reviewers
Subscribers: Korvin, epriestley, yelirekim
Maniphest Tasks: T11586
Differential Revision: https://secure.phabricator.com/D16541
