Make example NXreflection files more like base classes#19

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phyy-nx wants to merge 3 commits intomasterfrom nxreflections_tidy

Commits on Jan 30, 2020

Update thaumatin NXmx/NXreflections example files treating NXreflections as a base class (see nexusformat/definitions#727 )
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Rename DETAILS.rst -> README.txt
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Commits on Feb 5, 2020

Remove NXdials (see dials/dials#1124 )
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