problem in lib/sha256.h

[Paulie Pena IV]

To Whom It May Concern,

There seems to be an error in the sha256.h file.  It declares
SHA224_DIGEST_SIZE = 24, but 224 bits is not 24 bytes, it is 28 bytes.
 The comments in that file also say that it should be 28 bytes.

Thanks,
Paulie