Support typed arrays in iconv.decode

[LMLB]

This simplifies using browserified iconv-lite as a standalone library in environments without Buffer by also allowing callers to provide a typed array instead of a buffer.

Note that you can't directly access the Buffer shim from outside the iconv-lite browserify bundle by default. Right now (without this change) you would either have to build and load the Buffer shim separately, indirectly access the Buffer shim via the "constructor" property of a buffer object returned from iconv.encode, or make a custom bundle that exports both iconv and Buffer.

[ashtuchkin]

I see the problem, yes. On the other hand I can see how this can lead to unexpected behavior like this:

> const buf = iconv.encode("hey", "latin1");
> const arr = Uint32Array.from(buf);
> console.log(iconv.decode(arr, "latin1"));
'h\u0000\u0000\u0000e\u0000\u0000\u0000y\u0000\u0000\u0000'

Does it make sense to just reexport Buffer class and make the caller be responsible for transforming typed arrays?

[LMLB]

I have limited it to only accept 8-bit typed arrays, how is that?