Improving perfomance for JSON Lines format

[edy555]

This patch improves performance when loading JSON Lines format.

Loading JSON Lines cause significant slowdown and stop accepting keys, even if the length is moderate.
This situation can be reproduced like follows.

seq 10000 |  jq -cs '{"id":.[]}' | jnv

For visualization and suggestions, the entire long list is not necessary, but a partial list of some length is enough.
Therefore I have created simple patch.

• Give a limit length for arrays as loading JSON Lines format
• Add --limit-length option to be able to specify the length

I often deal with JSON-Lines files that have tens of thousands of lines, so I hope jnv can handle them comfortably.

[ynqa]

@edy555 Thank you. I've put a comment.

[ynqa]

@edy555 Sorry for my responses late... Commented about the short flag -s. Everything else LGTM.

[edited] Never mind this one, detailed at #41 (comment)

[ynqa]

LGTM!