Minor fix to generation of JSON file structure

Fix to generation of JSON file structure to handle more types of string dataset in the input NeXus file.

Release is on:

• Anaconda https://anaconda.org/ESS-DMSC/nexus-streamer
• PyPi https://pypi.org/project/nexus-streamer/0.2.1/

Add fake event data generation option

Changes:

• Fake event generation mode added. This is intended to be used for performance testing consumer applications. It can be used by providing the --fake-events-per-pulse <INT> argument.
• Include data units in generated JSON description of NXlogs to be published as f142 streams.

Available on conda and pypi:
https://anaconda.org/ESS-DMSC/nexus-streamer
https://pypi.org/project/nexus-streamer/0.2.0/

Minor fixes

Minor fixes to version handling in conda and pypi packages.

First release version

Most functionality that was present in the C++ implementation (https://github.com/ess-dmsc/nexus-streamer) is already implemented here, however these features are missing:

• ISIS-specific data when using a file from ISIS Neutron Source (detector-spectrum map and pulse info in each event message)
• randomly generated events (this mode is useful for performance testing consumer applications)

The release is available on anaconda: https://anaconda.org/ess-dmsc/nexus-streamer
and PyPi: https://pypi.org/project/nexus-streamer/