Add all_matches function

[adambom]

This should be used in cases where you want to match multiple instances of a pattern in a string using regular expressions. This is instead of adding a g modifier, e.g. r"abc"g.

Addresses #1487

[JeffBezanson]

This is not really regex-specific, and could be done more generally with [each_match(r,s)...]. But each_match already makes it easy to iterate over the matches, so you don't usually need them in an array.

[kmsquire]

This was in response to Stephan's comment in #1487.

[JeffBezanson]

In that case I also invite @StefanKarpinski to read my comment here :)

[StefanKarpinski]

Yeah, that's pretty much why I hadn't defined this, but all_matches(r,s) is a bit easier to read than [each_match(r,s)...], so the question is whether writing that is common enough that you actually want to have all_matches. I haven't much needed it myself, so it's a bit hard to say.