Npyscreen

Forms now automatically scroll to show as much of a widget as
possible, using a method called on_screen(). This method should be
re-factored to be more efficient. Currently it uses 4 while loops,
which, while they get the job done (geddit?) should really be if
statements instead.

To avoid calling without need, the refresh loop now sets a value
called ALL_SHOWN to true or false.

A wrapper to help edit multi-line text added: the StringToEditor
function and the MultLineText class. The latter is based on the
button, and can be seen in EXAMPLE.py. Neither have been stress
tested - Paul? - and so should be regarded as beta until the next
release.

Minor bug-fixes.

Internal changes to the multi-line widgets to make them more
flexible. An indication that there are items not shown on the
screen added. Designed to be space efficient, but do we like?

Internals of the Titled widgets cleaned up.

Internals of the Form wrapper changed.

Numerous cleanups. Some small documentation changes.
_Form object made easier to subclass by tidying up the edit loop.
Action to take when widget exits is now determined by a dictionary
lookup: see the set_up_exit_condition_handlers() and the
handle_exiting_widgets(condition) methods for details.