Add StringScanner class from https://github.com/zacharyvoase/strscan
Add StringScanner class from https://github.com/zacharyvoase/strscan

The StringScanner is a near-direct port of Ruby's StringScanner class.

Licensed under Public Domain

Signed-off-by: refnode <8b6a5d0d18592825657659ce5fd35c6e7a593ce0@gmail.com>
refnode/liquid,refnode/liquid