Minor improvements in some reading functions

Just a proposal with some minor improvements. The difference is almost neglectable on modern computers and very small even in low-end old hardware (like an Atom N270). Anyway, you can have a look at the performance [test results] (http://jsperf.com/read-unsigned-integer).

I did also some [tests] (http://jsperf.com/read-bytearray-to-string) to consider alternate methods to read strings from the byteArray. In this case, the best results are those obtained with the current functions, so, no changes proposed for string reading.