perf: improve performance a bit

[addaleax]

Use binary search rather than linear sort, since we already
have the ranges array sorted to begin with.

Also, use .splice() directly and avoid removing an element
and then re-introducing others.

[bcoe]

@addaleax this looks smart to me. As for our discussion today, I think this algorithm was already a bit broken, and might be fixed with using binary insertion rather than splice.

Should we do this separately? how many cycles do you feel like you have?

[demurgos]

This PR results in 20% shorter execution in my experience: merging yargs coverages 100 times goes from 4.7 to 3.85 seconds.

Edit: See #4:

upstream/master:
[email protected] x 23.11 ops/sec ±4.21% (42 runs sampled)
addaleax/improve-performance:
[email protected] x 29.26 ops/sec ±4.19% (51 runs sampled)