When no view_name is given, just display the context.

Do not try to get the immediate view ourselves.  This will let the
standard Zope and Plone machinery do its work.

Do the same when traversing to 'view' does not work even though
viewing this url works just fine.  That can happen in some cases.
Do not use deprecated clean_string from jquery.pyproxy anymore.

Requires jquery.pyproxy 0.3 or higher.
Note earlier move to zestsoftware github account.
Cleanup setup.py
Move version to setup.py
Move collective/sendaspdf/HISTORY.txt to CHANGES.rst.
Add MANIFEST.in and setup.cfg to control releasing.