node 0.4.2 buffers vs strings problem causes broken int and float decoding

ints and floats are not unpacked correctly under node 0.4.2 due to conversion of input data from a binary buffer to a string in _readString() method. the 'rest' return value, should remain a binary buffer, and substr() and substring() calls in other _read{Int,Float, etc} functions should be replaced by slice().

I fixed this in my fork but being a github noob I'm not sure what else to do about it
