Refactor parsers submodule

Refactor parsers submodule to simplify the creation of all the different parsers.

4 parsers exist: MainParser, SubCommandParser, help Parser, common Parser. Are they all needed?
Fix triple quoting indentation. Fix formatting of multiline triple quotes with \n chars. Confirm automatic dedentation in triple quoted strings.
Replace classes with function calls? (simplify the code)
Merge modules into single module?
Cleanup formatting parentheses in callback_function()
Simplify the logic?

ACCESS-NRI / amami