Disallow zero sized types

[fselmo]

What was wrong?

• Solidity doesn't support empty structs / tuples; we should not support them in eth-abi.

How was it fixed?

• Validate against zero-sized tuples and provide a good message for these errors.
• Add tests and update current tests for empty tuples.

Todo:

• [x] Clean up commit history
• [x] Add entry to the release notes

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The Sunda Colugo