Bug fixes and additional utilites, and build env fixes

An important update that includes a bumpy to python 3.9 and important updates to the build environment to avoid potential incompatibilities with the numpy C API between build/runtime environments that was seen for the latter 0.8.16 conda packages.

What's Changed

• added docstrings for Euler functions by @joelvbernier in #363
• Revert fixed conda version by @cjh1 in #365
• Bump to Python 3.9 by @cjh1 in #364
• Added list sort to deal with glob by @joelvbernier in #367
• Update imagefiles.py by @joelvbernier in #369
• Pin numpy to version 1.20 by @psavery in #370
• Change numpy==1.20 to numpy<1.21 by @psavery in #371
• Update fitpeak.py by @darrencpagan in #372
• make darren's updates PEP8-compliant by @joelvbernier in #373
• Use skimage for center of mass instead of scipy by @psavery in #374
• added auto powder cal classes by @joelvbernier in #375
• Fix conda numpy version to 1.20 by @psavery in #378
• Rotations features by @joelvbernier in #377
• Try fuzzy constraint for numpy version by @psavery in #379

Full Changelog: 0.8.16...0.8.17