Avoid using the quote character (") in our chunk encoding.

This quote character requires escaping in JSON strings, and using
it for BLOCK_DIRT was causing the average chunk to be somewhere on
the order of ~50kb. This patch corrects that problem by increasing
the lower number to above that of a quotation mark, reducing the
average chunk size back to ~33kb. Ideally we will apply compression
and base64 in the future for even more space savings, but that's a
bit more involved (see https://github.com/crazy2be/compression-tests)
Merge pull request #145 from crazy2be/feature-faster-chunks

I feel like using compression wouldn't be that much harder, there is no real point in doing these minor things to reduce the size, we should just do LZW compression, which will probably get us 99% reduction for a few dozen lines of code.

But sure, there is nothing wrong with accepting this now that it is done.