Added UnusableAppenterException and some examples

ADDED:
- UnusableAppenterException
- TextAppenter.UNUSABLE
- NewTextAppenterFor.UNUSABLE
- com.github.xbn.examples.io.TextAppenterObjectDebugging and
TextAppenterWithLevelsAppExample

NEW MINOR ISSUE: The output for the above examples is manually copy and
pasted. Something about them writing indirectly to the console (via
TextAppenter.CONSOLE) is not working properly via Codelet. Executing the
example directly works fine.