Run search in parallel

[andrusha]

On SSD random-reads are cheap and running threaded search probably would result in better performance. Also it's a great exercise to do in Go anyway.

[xarg]

I thought of it myself, but it didn't make sense for my disc and I don't have an SSD to test this on. Fortunately it's not complicated to add more parallelism to this. I'll check this out.