bug#701 - partial fix

This patch resolves issues with how call writers merge their instructions into
the main handler instruction list.
- writeCalls will now only merge instructions into the list of the next higher
  call writer
- all call writers have been given a finalise() method to use when the call
  writer needs to be terminated gracefully at the end of parsing when the wiki
  markup didn't provide its expected exit syntax.

I have only tested finalise with lists. It still requires testing with wiki markup
which results in improperly closed tables, quotes and preformatted text (it may
not be possible to improperly terminate some of these syntax modes).

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