Fix base convert issues (PHP on IIS and possible other issues)

I had run into an issue where my keys would not validate on my IIS server using PHP but worked fine on Apache.

I fixed this by replacing the base_convert function with this one.

gist.github.com/bagelxjames/6b63b98 ...

In the license_key.class.php file:
-Do search/replace for "base_convert" to "$this->str_baseconvert"
-Then copy and paste the function posted into the class

(so you don't replace the base_convert function inside str_baseconvert)

I found this gave me perfect results across all platforms.