Support for Enum Types in ABI Generation

[0x19]

This pull request introduces the ability to recognize and handle enum types in our ABI generation process. This is a crucial addition as enums are a common feature in Solidity contracts, and their omission in our ABI generation process was a significant gap in our functionality.

The changes in this PR include:

• Enum Type Recognition: We've added a new function isEnumType that checks if a given type is an enum. This function is used during the state variable injection process to correctly identify enum types.
• Enum Definition Parsing: We've extended the AbiListener with a new method EnterEnumDefinition. This method is called when the parser encounters an enum definition in the Solidity code. It extracts the enum's name and its values, and stores them in the AbiParser's map of defined enums for future reference.
• Enum Handling in State Variable Injection: The InjectStateVariable method has been extended to handle enum types. When an enum type is detected, the method now correctly generates the ABI for the enum.

This pull request references issue: #6

[coveralls]

Pull Request Test Coverage Report for Build 5430959025

• 35 of 35 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+1.9%) to 65.196%

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Totals
Change from base Build 5430775659:	1.9%
Covered Lines:	399
Relevant Lines:	612

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💛 - Coveralls