Various DRISL features #698

Hello,

I am developing a library that implements the DRISL spec, formerly known as dag-cbor. To reach strict compliance with that spec, I had to fork this repo and add a number of features. I wanted to open this issue to get feedback on whether any of the features are upstreamable, rather than bombard you with multiple issues.

My fork is available here, however I know the patches are not ready for submission yet. If there is interest in any of these features I will improve their quality and submit a PR.

Features

• Prevent decoding floats unless they are encoded as float64
• Only encode 64-bit floats (converting other float types)
• Prevent encoding of big nums while still accepting big.Int if it fits in a CBOR integer
• Restrict map encoding to string keys
• Don't decode null map keys or tagged map keys
• Disable keyasint feature
• Prevent encoding/decoding arbitrary simple values
• Limit tag decoding to only those that have been provided in a TagSet
• Only decode integers encoded with preferred encoding
• Enforce map sort on decode
• Don't encode time.Time at all
• Limit integer range to int64 min/max (encode and decode)
• Ban floats entirely

All features are behind an encode or decode option.

Let me know what you think of any of these!