[WIP] Implemented a Code Formatting Codegen Module

[jalextowle]

Description

These changes add a module to the solfix crate that will do very basic code generation. This code generation consists of turning a provided ParseTree into a formatted string that is a valid Solidity file.

Future Enhancements

• Add a maximum line number to the style rules that will try different rules if the first rule generates a string that is over the maximum line number.
• Accept a configuration file that specifies the strings that should be output once a keyword is matched.
• Accept a configuration file that specifies style rules (this is likely difficult)