Utf8 strings

To close this issue: https://github.com/vibornoff/asmcrypto.js/issues/59

SHA1, SHA256 and SHA512 did not work as expected with utf8 strings

eg

    $ echo -n "This string contains UTF8 characters - Ͼ" | sha1sum
    9ace614c96c229d38b2143f6b165f775cc552740
    asmCrypto.SHA1.hex("This string contains UTF8 characters - Ͼ")
    "3c0231663fc23ce32480e0c70e29f860bcff7f6e"

This pull request ensures the hash is correctly computed for utf8 strings.