Version Two: Support for cross-realm strings & '0'

Versions 1.x considered a string containing only whitespace and the character 0 to be empty, which doesn't match up with common expectations. In addition, versions 1.x chose performance over universal support in it's implementation of determining if a value was indeed a string or not. This new release takes a commonly accepted performance hit in order to ensure accuracy & usability across realms, e.g. when code is used across iframes.