hashsum Incremental Binary Read Fix for #303

hashsum no longer converts files to UTF-8 for digest.
hashsum now reads binary data only.
hashsum now reads files incrementally using a 512KB buffer.
hashsum now properly writes the binary indicator based on
    user input. Notice that all files are in binary mode
    regardless of the flag set by the user.

Gil Cottle <gcottle@redtown.org>