Efficient addArray method

[tomijaga]

An efficient solution for the addArray() method addressed in this comment
#368 (comment)

The previous solution used the add() method, which could resize the array more than once.
This PR solves this problem by only resizing the buffer once.

[ghost]

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[matthewhammer]

Thanks for this PR!

Seems very reasonable, except the API is getting large and presenting lots of choices to the programmer now.

The situation addressed here is adding an array to a buffer. They could either use this proposed functionality, or use what is there now in two steps: (1) create a second buffer from their array (via newly merged Buffer.fromArray) and then (2) add entire buffer that via the existing Buffer.append.

The upside of this two-step approach is that it does not require growing the API of the Buffer class, which will enlarge the representation of every buffer instance.

The downside is that the two-step approach will not avoid the extra resizing, which is the whole point of this PR.

But to address that, we could try to absorb some of this clever logic here (Buffer.fromArray could be constant time, with some extra work, and Buffer.append does not do anything clever now, but it could do something like this PR is doing).

WDYT?

[tomijaga]

I think it would be a great idea to add the functionality from this PR to the Buffer.append method. It will improve the buffer without increasing its API.

I'm curious, however, about how Buffer.fromArray would be implemented at constant time. The method that comes to mind is to pass the array as a parameter in the constructor, but that would create a breaking change. It would be interesting to see how it's implemented.

Regarding the update for the Buffer.append method, would you like me to create a new PR with the new logic?
@matthewhammer