adds performance improvements

[kgwinnup]

This PR makes three performance related changes:

1. instead of using the standard parseInt to parse the string TLSH hash into a byte array, a custom string to base 16 function is implemented.
2. When splitting a leaf, the loop now properly exits when the TLSH distance (splitPoint) grows greater than 255
3. Minor tweak to the incrementing of the splitPoint, and starting split. (empirically these values are decent, but may be specific to a use case, may want to consider these as a parameter in the future).