Cleaned up and optimized wfBaseConvert();
* Added code to use BCMath or GMP if they are
loaded, since they are both significantly faster.
A parameter was added that can be used to force
usage of a specific engine (mainly for testing).
* Made an array of base digits rather than using
strpos() every time.
* Used casting instead of intval(), since the latter
is six times slower.
Also added unit tests for wfBaseConvert as well as
a benchmarking class that measures the difference
between using GMP, BCMath, and pure PHP.
Change-Id: I841717be2b29a0b7fc57a13fde5cc0642cda82df