Support Non-ASCII Characters for User-Provided String

[charitylxy]

• [x] This contribution adheres to CONTRIBUTING.md.

What does this Pull Request accomplish?

This PR aims to address the issue brought up in https://github.com/ni/nidaqmx-python/issues/384 and https://github.com/ni/nidaqmx-python/issues/384

• Currently, user-provided strings only accept ASCII characters.
• This change will allow non-ASCII characters for user-provided strings.

Why should this Pull Request be merged?

• Argument with String type are now encoded to UTF-8 to fix the issues:
  • https://github.com/ni/nidaqmx-python/issues/384
  • https://github.com/ni/nidaqmx-python/issues/20

What testing has been done?

Manually tested on command line with non ASCII string argument.

>>> import nidaqmx.system
>>> d = nidaqmx.system.Device ("장치")
>>> d.serial_num
0

[charitylxy]

Not sure if it's appropriate to still load nicaiu.dll while encoding strings to utf-8 but seems like it's working on my end even without changing it to nicai_utf8.dll.

[charitylxy]

Adding python-decouple dependency in https://github.com/ni/nidaqmx-python/pull/524. Regression tests will fail for now until https://github.com/ni/nidaqmx-python/pull/524 is merged in.