feat: add NFT standard

nft-standard.md

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+## Preamble
+* Sip Number: 009
+* Title: Standard Trait Definition for Non-Fungibe Tokens
+* Author: Friedger Müffke ([email protected])
+* Consideration: Technical
+* Type: Standard
+* Status: Draft
+* Created: 2020-12-10
+* License: CC0-1.0
+* Sign-off:
+
+## Abstract
+Non-fungible token are unique digital assets that are registered on the Stacks blockchain through a smart contract with certain properties. 
+Users should be able to identify a single non-fungible token. Users should be able to own it and transfer it. Non-fungible tokens can have more properties 
+that are not specified in this standard.
+
+## License and Copyright
+
+This SIP is made available under the terms of the Creative Commons CC0 1.0 Universal license, available at https://creativecommons.org/publicdomain/zero/1.0/
+This SIP’s copyright is held by the Stacks Open Internet Foundation.
+
+## Introduction
+
+
+## Specification
+
+```
+
+(define-trait stacks-token-nft-standard-v1
+  (
+    ;; Name, limited to 32 chars
+    (name () (string-ascii 32)) 
+
+    ;; Icon URL, limited to 2048 chars
+    (icon-url () (string-ascii 2048))
+
+    ;; Token ID, limited to uint range
+    (last-token-id () uint) 
+
+    ;; number of tokens owned by user
+    (get-balance (principal) uint)
+
+    ;; Owner of given token identifier
+    (get-owner? (uint) (response principal (tuple (kind (string-ascii 32)))))
+
+    ;; Transfer from to
+    (transfer? (principal principal uint) (response bool (tuple (kind (string-ascii 32)))))
+
+    ;; Approve
+    (approve (principal uint) (response bool (tuple (kind (string-ascii 32)))))
+
+    ;; Set approval for all
+    (set-approval-for-all (principal bool) (response bool (tuple (kind (string-ascii 32)))))
+
+  )
+)
+```
+## Related Work
+
+## Backwards Compatibility
+
+## Activation
+
+## Reference Implementations