T1dOpeningOMEXML: clean up style and comments
T3aDiscoveryTutorial: clean things up

In particular, we don't want to encourage people to annotated their
Format plugins with the narrowest possible type, because then SezPoz has
to load the class at discovery time, instead of it being able to happen
lazily when the Format first needs to be instantiated.
T3bCustomFormats: clean up comment formatting
Merge branch 'tutorial-updates'

This branch updates the tutorials with formatting and style fixes.

It also updates T3aDiscoveryTutorial's language and code samples
to be consistent with current thinking.