add FindTagsAppend()

[pforemski]

I suggest a FindTags() version that can minimize memory allocations, which is implemented in this PR.

The PR introduces FindTagsAppend(), which uses a destination slice instead of allocating it inside the function. The slice can be pre-allocated by the caller, and re-used between successive calls.

[wblakecaldwell]

Thanks @pforemski. Good idea, I'll take a look. Sorry for the delay - I need to update my GitHub notifications :)

[pforemski]

Any chance to merge this anytime soon? I'd love to go back using the mainstream repo ;)

[wblakecaldwell]

@pforemski This is really great stuff - thank you so much. I took your idea and ran with it.

I'm not maintaining backwards compatibility. It'll require minor changes to update, but everyone's performance will improve because of it. I just converted the FindTags to your FindTagsAppend, updated FindDeepestTags and FindTagsWithFilter in the same vein, and added a buffer parameter to the Delete method.

While I was at it, I got rid of the unused error return values - as you noticed, they're all returning nil anyway.

Check this out - old code vs new on Intel(R) Core(TM) i9-8950HK CPU @ 2.90GHz in a VM:

BenchmarkFindTags-5                     	 3721257	       294.3 ns/op	     160 B/op	       6 allocs/op
BenchmarkFindTags-5                     	41273214	        28.12 ns/op	       0 B/op	       0 allocs/op

While I'm evaluating all of this, it's sitting here: https://github.com/kentik/patricia/tree/wbc-fewer-allocations, in this PR: #14

Have a look if you're interested, I'd love your feedback.

[wblakecaldwell]

PR accepted with additions in this one #14

Thanks for the submission!