Fix snow.platform.web.utils.ByteArray resizing

[restorer]

In my app ByteArray has very slow performance while reading big json file.
I dig into this problem, and found that set_length calls _snowResizeBuffer at every writeByte.
Illustration:

value	allocated	action
-	0	initial
1	1	up resize
2	2	up resize
3	4	up resize
4	4	-
5	8	up resize
6	6	down resize
7	12	up resize
8	8	down resize
9	16	up resize
10	10	down resize
...	...	... etc ...

My proposal is to do down resize if allocated are twice more than required value.

[ruby0x1]

I might not have been properly clear in the dev log, but this class and everything associated with it is being deleted during alpha-2.0 in favour of newer code. Nice catch though!

http://snowkit.org/2015/03/01/snowkit-dev-log-1/