use string buffer for IO read, it speed up parsing and at the same time fixes crashes for big buffers sizes
use string buffer for IO read, it speed up parsing and at the same time fixes crashes for big buffers sizes

Signed-off-by: Brian Lopez <0ec80f4c8755db004f2dde2ee9cd355843d6236d@gmail.com>

sferik/yajl-ruby,sferik/yajl-ruby,sferik/yajl-ruby,brianmario/yajl-ruby,tenderlove/yajl-ruby,tenderlove/yajl-ruby,brianmario/yajl-ruby,brianmario/yajl-ruby,mrkn/yajl-ruby