Fix endianness of input array

Our sha1_buffer function returns the output buffer in byte-wise little-endian
order; in order for our comparison of input and output (memcmp) to work
correctly, our input array has to use the same order.
Thus I fixed all parts of the code touching any of the SHA arrays (e.g. string
to sha, print sha, increment input, etc) to conform with this new little-endian
order.