Constructor
new()
Replaces a string's "master string" — the string it was built from —
* with a single character to save memory. Find more information about this AS3 oddity
* <a href="http://jacksondunstan.com/articles/2260">here</a>.
*
* @param str String to clean
* @return The input string, but with a master string only one character larger than it.
* @author Jackson Dunstan, JacksonDunstan.com