Fix, minor refactoring and TSDocs (naddison36#123)

chore: refactor functions that convert AST types to UML Class types
chore: started adding TSDocs
chore: Operator.isPayable changed to Operator.stateMutability
chore: updated dependencies
chore: bumped version to 2.3.1
fix: missing associations when emitting events

lib/converterAST2Classes.d.ts

@@ -1,3 +1,10 @@
 import { ASTNode } from '@solidity-parser/parser/dist/src/ast-types';
 import { UmlClass } from './umlClass';
+/**
+ * Convert solidity parser output of type `ASTNode` to UML classes of type `UMLClass`
+ * @param node output of Solidity parser of type `ASTNode`
+ * @param relativePath relative path from the working directory to the Solidity source file
+ * @param filesystem flag if Solidity source code was parsed from the filesystem or Etherscan
+ * @return umlClasses array of UML class definitions of type `UmlClass`
+ */
 export declare function convertAST2UmlClasses(node: ASTNode, relativePath: string, filesystem?: boolean): UmlClass[];