prjemian/spec2nexus: 2.1.0

• #135 switch to semantic versioning
• #133 support user control line "#U " with plugin
• #131 support #MD control lines from apstools.SpecWriterCallback
• #125 fluorescence spectra in files for RSM3D
• #120 do not mock six package in documentation
• #119 delimiters in #H/#V lines with or without text values
• #116 process data from spock

see release notes

It takes a couple steps to upgrade an existing conda installation from version 2017.nnnn to newer version 2.1.0

• add a declaration of spec2nexus < 2000 in the conda-meta/pinned file in the conda environment
• conda update -c prjemian spec2nexus (should change to 2.1.0)

It may still be necessary to uninstall and reinstall spec2nexus to effect an update:

conda uninstall -y spec2nexus
conda install -c prjemian spec2nexus