declaration extractor/struct fields and syntax checks

[jermy-c]

Fixes #

Changes:

• rename declaration_extraction to declaration_extractor
• improve naming
• add StructFields extraction
• support method functions
• syntax checking
• support for multiple package declarations
• support for package declaration on other lines
• support for flexibility of space or no space between ([inputs])([outputs])
• support for imported types, variable like ast.CXArgument
• fix tests to use functioning CX programs
• support for pointers
• add TypeDefinitionDeclaration
• support for arrays/slices
• fix keywords in string issue Does this change need to mentioned in CHANGELOG.md?

[kenje4090]

Nice work