Added an overload for countUntil to increase performance by up to 2x

Also, there was apparently a lone tab way down in the file, so that is now 4 spaces.

Ignoring the name of the branch (I realized after I created it that it was a bad name for it), this basically just adds an overload which uses a memchr to locate data in an array. In my tests, this produced a 2-3x performance boost. I'll end up not actually using it myself due to the fact I was able to get a 4x boost by using strlen instead, but I thought this is probably worth getting into the standard library due to the boost in performance.
Must check if T is a struct and has overloaded opEqual. See `std.traits`.