Maj change - functions to create & close DDE conv

Changes:
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1. Simplified helper functions to easily and quickly create and close
DDE communication link objects. Interface functions added include
pyz.createLink(), pyz.closeLink() and link.close(). In order to support
the simple interface, some code was added for internal processing.
2.  Changed ipzCaptureWindow2 to ipzCaptureWindow, and renamed the low
quality image capture function to ipzCaptureWindowLQ
3. Code refactoring in several places, made more Pythonic.
4. Several zGetxxx functions were modified to return namedtuples instead
of tuples for better human understanding. (Not all functions are
converted; however, this is an ongoing process)
5. Bug fix. A small bug was introduced in the previous version (v0.7.5)
in the function spiralSpot() when the list comprehensions were converted
to generator expressions. The generated values of theta were getting
consumed at twice the rate of consumption of 'r' since both 'r' and
'pXY' were requesting for 'theta' from the same source.