Add a constructor with size parameter on JSONArray and JSONObject classes

[SuperPat45]

JSONArray is initialized with an initial size of 10, but if I know in advance that I have hundreds of elements, a new constructor with an initial size can avoid lots of arraycopy under the hood.
Conversely, if I know I have less than 10 items, it could save memory.

Idem for JSONObject

[UrielCh]

Easy to improve, and should not beak anything else, feel free to open a PR, I'm okay with this change.

[hezhangjian]

@SuperPat45 @UrielCh Sorry for my late reply, I have already create PR for this.

[hezhangjian]

@SuperPat45 the PR has been merged, free feel to tell me if you want a new release