The SHA4 name was not clear with regards to the new SHA-3 standard. So
SHA2 and SHA4 have been renamed to better represent what they are:
SHA256 and SHA512 modules.
More fixes based on the compiler directives -Wcast-qual -Wwrite-strings
-Wmissing-prototypes -Wmissing-declarations. Not everything with regards
to -Wcast-qual has been fixed as some have unwanted consequences for the
rest of the code.
