Branch providing a safe implementation

[victorporof]

I suggest having a branch in this project with a safe implementation that never touches the String prototype.

I've looked into augmenting the default implementation on master with an option to avoid touching the String prototype on import, but afaict that cannot be easily done at the moment without significant code duplication, but as it stands it seems that this library is intended to also be used as a drop-in in browser environments without a webpack, browserify or even some sort of concatenation build step.