Implements string replace method and testing

[HendersonSC]

Implements %replace() method as a generic. One implementation takes a starting index and optionally a stopping index replacing everything in between with repetitions of a supplied character pattern. The other replaces all occurrences of a specified pattern with a replacement pattern.

To do this it became advantageous to implement %split() generically as well. The first implementation, without arguments uses a single space as the delimiter and consumes consecutive delimiters returning an array of strings containing no empty strings. The other implementation utilizes a user supplied delimiter. This does not consume consecutive delimiters and instead returns a string array which may contain empty strings where consecutive delimiters occurred. If the delimiter is not found then both implementations will return a size 1 array containing the original string.

This aimed to be a functional mirror of the python method by the same name.

[aarograh]

I'm good with the current set of changes. Downstream codes will need some minor updates before deleting strrep. I'll make an issue to do so once those codes are updated.

@stimpsonsg Can you merge?