Escape formatting should escape slash

[jcubic]

Issue summary

It's problematic if you echo stuff and you want to echo single slash \, escape formatting don't work because it only escape [ and ]

Expected behavior

Single escape should be enough to render anything

Actual behavior

formatting is broken if you echo single slash in formatting even using escape_formatting.

Steps to reproduce

1. Open Pipe demo
2. Type fortune | say | lolcat --bug