Create sha256 mask

We should also create a DataMask that does sha256 of the data:

• strings should be sha256 of the utf-8 representation of the string represented as hex digits
• binary should be sha256 of the binary in binary
• integer types should be sha256 of the little endian representation of the number in little endian cut down to the right size (1,2,4, or 8 bytes)
• floating point types should be sha256 of the binary representation as either 4 (float) or 8 (double) bytes
• timestamps and dates should convert like integers
• decimal should convert like 128 bit numbers with the result cut to the matching number of bytes

It isn't clear what we should do in the very small data types:

• boolean
• byte
• short

I'd lean toward either making them null or passing them through unchanged.