Revised sha*.py source for redundancies.

Parsed sha1.py, sha256.py, and sha224.py source for redundancies/unclear
syntax. Firstly, removed ctypes.c_uint objects where
flooring the stored value (by mod 2**32) was unnecessary. Then replaced
ctypes.c_uint usage entirely by "& 0xFFFFFFFF", before switching to
simply "% 2**32" (for brevity's, and newbie readability's, sake).
Removed print messages at the end of each file (used to debug), and
deleted the hashlib/ctypes import statements. Further commented-in code
to describe certain operations.