Update compliance with IOG spec

[gtrepta]

We need to break down the changes that were made to the Plutus specification since milestone 1 up to the version of the spec as of July 26th.

[gtrepta]

Changes made on April 27th:

• [x] Appendix A: Note 1 now says the four integer division functions fail when the second operand is 0, instead of negative.
• [ ] Section 3.3 adds a paragraph with the note we assume throughout that the body of a Plutus Core program is a closed term. It states that the program should be checked before execution and rejected if it isn't closed.

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• [ ] The section on flat encoding now states that Integer and Bytestring encodings of Data are restricted to a maximum of 64 bytes, and that their tools will reject anything larger during deserialization. In the 7/26 spec this is stated in the CBOR encoder section during the introduction.

Changes made on May 20th:

• [ ] A section for builtin functions added by the Cardano Vasil release.

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• [x] The verifySignature function is renamed to verifyEd25519Signature (because Vasil introduced other signature functions).

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Changes made on June 14th:

• [ ] Appendix section for the flat format was overhauled

  73

Changes made on July 14th:

• [x] A new appendix section was added for CBOR encoding

Changes made on July 21st:

• [x] The note on bytestring comparisons in Appendix A was updated for the case where a bytestring is empty.

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Changes made on July 26th:

• [x] The definition for $V \sim \iota$ was updated in Figure 5 to specify polymorphic type variables can only be instantiated by any builtin type (and not any type at all)

[SchmErik]

I implemented the CBOR decoder according to the July 14th version

[SchmErik]

Flat format has been implemented but this was before 7/14. I'll check my implementation against the spec to see if I'm missing anything.