Add Major Only Split Support

• Adds support for splitting a currency amount string with only major and currency code.
• Adds test case for the single argument split function.
• Fixes the unit test using the system decimal point.
• Updates the unit test structure to the normal catch2 form.
• Changes from "pragma once" to if/defs since it's a library and may encounter issues with some peoples set-ups.
• Removes code no longer needed for currency amount splitting.