Implicit IVs

Good morning sunshine! This PR will add the implicit IVs make the developer's live simple, I guess

I would like to send a separated PR to remove encoders and make it implicit too. The idea is to make utf8String encoder the default so my solo idea is:

- Before:

        var options = {
            IV: hex.toBits( BOB_IV ),
            AAD: hex.toBits( BOB_AAD ),
            key: rawPassword,
            data: utf8String.toBits( PLAIN_TEXT )
        };

- After (defaults to utf8String):

        var options = {
            IV: BOB_IV,
            AAD: BOB_AAD,
            key: rawPassword,
            data: PLAIN_TEXT
        };

If for some reason developers are willing to use Hex codec, my proposal is:

    var options = {
        IV: BOB_IV,
        AAD: BOB_AAD,
        key: rawPassword,
        data: PLAIN_TEXT,
        codec: sjcl.codec.hex
    };