request to support PCRE_PARTIAL_SOFT

[jdar]

One use-case for embedded systems would be accepting user input, and generating events based on those incremental changes in user input. PCRE supports this type of partial matching.

While normal ruby regex does NOT do partial matching, Regex implementation is not exactly part of the spec. So it might be acceptable to add as an option.

I would volunteer to try to implement if you think it's a good idea.