Move api diff logging to its own method.

Move logic responsible for logging API diffs into separate method
which improves code clarity by not cluttering the logic of the
`changedIncrmenetal` method.

Also, switched to proper methods in `Logger` when logging exceptions.
Removed `StackTrace.full` which turned out to be not needed becuase
sbt offers an option to log the full stack trace by enabling
it through configuration.