Support more naming conventions for symbol names

[UsernameFodder]

Some other sources use symbol names with hybrid naming conventions. Add support for a few more sensible conventions in resymgen, and loosen the restrictions for pmdsky-debug function names to include Pascal_Snake_Case (multiple underscore-delimited PascalCase parts).

Support for the following new naming conventions has been added to resymgen for general use:

• camel_Snake_Case (camelCase_Then_PascalCase)
• underscoreSeparated_camelCase
• Pascal_Snake_Case (UnderscoreSeparated_PascalCase)
• flatcase
• UPPERFLATCASE

[UsernameFodder]

@AnonymousRandomPerson FYI