v3.0.0

Change the internal method of saving errors entirely to make use of errors.As and errors.Is, removing the need for 3 separate methods as suggested in #7 by @bkmeneguello and implemented in #8.

V3 migration guide

V3 completely revamps the ErrorRegistry and now utilises the errors package to match errors.
The following changes have been made:

• RegisterErrorHandler now requires a concrete instance of the error as its first argument
• RegisterErrorHandlerOn now requires a concrete instance of the error as its second argument
• RegisterStringErrorHandler has been removed, use static errors.New in RegisterErrorHandler to get this to work
• RegisterStringErrorHandlerOn has been removed, use static errors.New in RegisterErrorHandlerOn to get this to work
• RegisterCustomErrorTypeHandler has been removed, wrap unexported errors from libraries to create handlers for these
• RegisterCustomErrorTypeHandlerOn has been removed, wrap unexported errors from libraries to create handlers for these
• ErrorRegistry changes:
  • DefaultCode has been removed, use RegisterDefaultHandler instead
  • DefaultResponse has been removed, use RegisterDefaultHandler instead
  • SetDefaultResponse has been removed, use RegisterDefaultHandler instead