Describe the bug

@kkoreilly please edit to clarify this as needed -- just a prompt to remember to fix this:

• If you define types and code without a main() function, the code will not run.
• Therefore, main is automatically inserted by yaegicore for Go
• But not for Goal, but we should enable it for Goal as well
• When you want to define a custom type with methods (such as for custom widgets), you can make your own main function for the main code so that things work properly (yaegicore only adds a main function if there isn't already one).

How to reproduce

Example code

Relevant output

Platform

macOS