Display type and callstack of exception on handler

This commit changes the Exception instance of SomeException to *simply*
display the underlying exception in `displayException`. The augmented
exception message that included the type and backtrace of the exception
are now only printed on a call to `displayExceptionWithInfo`.

At a surface level, existing programs should behave the same since the
`uncaughtExceptionHandler`, which is responsible for printing out uncaught
exceptions to the user, will use `displayExceptionWithInfo` by default.

However, unlike the instance's `displayException` method, the
`uncaughtExceptionHandler` can be overriden with
`setUncaughtExceptionHandler`. This makes the extra information opt-in
without fixing it the instance, which can be valuable if your program
wants to display uncaught exceptions to users in a user-facing way
(ie without backtraces).

This is what was originally agreed for CLC#231 or CLC#261 with regard to
the type of the exception information.

The call stack also becoming part of the default handler rather than the
Exception instance is an ammendment to CLC#164.

Discussion of the ammendment is part of CLC#285.