Refactor human readable abi parsing

[mattsse]

This includes a more sophisticated human readable abi parser that should be on par with ethers-js's interface parser.

Motivation

The existing parser followed the grammar loosely;
False positives were possible, so that for example event SetValue_function_called() would be detected as Function.

Solution

All parser function are replaced with a handwritten parser that follows ethers-js abi parsing rules.
This also detects StateMutability and constructors.
All tests are successfully updated with the new parsers.

Up for discussion

• mandatory returns statement: The new parser will fail if a function lacks a returns statement before its outputs. The contract_human_readable example did not succeed because a missing returns statement (function getValue() external view (string)) was detected and fixed in #
  f3bd156 . I'm not sure wether the preferential behavior would be to allow a missing returns or require it. ethers-js treats a missing returns before ouputs as an INVALID_ARGUMENT exception.
• error handling: This introduces a lot more error checking. Right now there is not a lot feedback about what was the root cause of an error, most of the time a simple ParseError::ParseError(super::Error::InvalidData) is returned. I'm open to make this responsive by introducing a Message(String) error type or provide the ParseError::ParseError(super::Error::Other(anyow::Error)) with a message.
• Side effects of constructor parsing: constructors are handled as Constructor now and asigned to Contract::constructor, I'm not sure about potential side effects of the constructor now missing from Contract::functions

[gakonst]

Amazing, thank you.