Ability to turn off JSON pretty printing and sorting of keys for better performance

[nikolaikrill]

SourceKitten can be quite slow in printing large number of code completion results. For example when importing Foundation:

sourcekitten complete --text $'import Foundation\n' --offset 18 -- -sdk macosx

On my machine, this example takes about 1.7 seconds. I've discovered that most of this is due to pretty printing and sorting of the JSON results, which is arguably unneccessary in most cases.

Rebuilding sourcekitten without the [.prettyPrinted, .sortedKeys] options in JSONOutput.swift reduces the runtime of the above command to 0.92 seconds, a significant improvement.

Please add an option to disable these printing modes. Thanks!