add str2argv.c/.h for advanced hook syntax.

Alexander (asac) Sackrequested to merge
advanced-hook-commands-w-str2argv into stable-3.0-BASE-2c5c780762981a5cfe699670c91397e29f6f6516

add str2argv.c/.h from https://github.com/ryanflannery/str2argv/blob/bbf8f669dd672f70bba5c2a307ce7a7e16308d03/

hooks are now split properly with str2argv so you can use more advanced commands like:

/bin/sh -c "run something; run something else; ..."

and not just simple single commands...

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