Separate Extension Rectification

[Lewiscowles1986]

https://github.com/Lewiscowles1986/WordPressSVGPlugin/blob/master/index.php#L83,L85

This is too detail oriented for a library with purpose to bring SVG support to WordPress. It also currently throws a warning in some PHP configurations as mentioned in #23.

Separate implementation to external dependency, possibly using composer autoloading.

This will also require a different release or upload format if using composer (bundled with frozen deps), and would benefit from #5 for all parts as well as #25