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 <refnode@gmail.com>
Add new Lexer class based for String scanning

Required for implementing the liquid parser class.

Signed-off-by: refnode <refnode@gmail.com>