Less obtrusive, configurable busting

The original package requires a user of this package to modify his templates in order to bust cache, e.g.: all occurences of HTML::script must be replaced with HTML::scriptBust. This is too obtrusive in my opinion, which I why modified the package to work without users of this package having to update their original code.

This merge will allow a programmer to enable or disable cache busting for his entire project with a single configuration change, or per environment. It also enables him to whitelist bustable file-extensions and (kind of) format the cache buster string.

All the changes are backwards-compatible according to your tests, so it is still possible to use HTML::scriptBust if one prefers that.