Fix issues 40 and 42 for the Python DAQmx API

Fix issue 40: is_task_done() cannot be used.
#40

Fix issue 42: register signal event not supported?
#42

Fix Issues 1 and 32

Fixing incorrect property data type metadata in the Python DAQmx API.
#32

Working around issue where nidaqmx doesn't work on Python 2.7.13 because of a ctypes bug.
#1

Add lock around `argtypes` to prevent race condition

Adding lock around argtypes to prevent race condition between setting argtypes and calling functions, in cases the functions run in parallel.

Some special cases needed unconditional locks around both the setting of argtypes and the actual function call, like the variadic power-up state functions in system.py, and the register events functions in task.py.

Fix Unregistering Callbacks and Miscellaneous Issues

Merging pull request - "Fix for unregistering callbacks"
#15

Fixing issue - "Should _import_lib error for unsupported platforms?"
#13

Fixing issue - "Cannot catch load/version issues with public API"
#12

Fixing issue - "CONTRIBUTING.rst link to Issues is broken"
#11

Minor release containing bugfixes

Update setup.py description and fix issues 2, 3, 5, and 6 raised by Ed Page.

• Splitting joined acronyms AIADC, AIDC, AILVDT, AIRVDT and CITC.
• Adding link to LICENSE file.
• Updating README.rst file in source directory to eliminate Sphinx domain directives and add link to documentation on readthedocs.

v0.5.0.post9

Initial release of nidaqmx.