Moved "Trial Query" Diagrams into "engineering" Subdirectory
Began Writing "Engineering" Documents

It's a WIP. Don't expect it doesn't break things.
Update IndexedPiece; Add AggregatedPieces

Add a new data model corresponding to results from a set of IndexedPieces.

Re-add "experiments" to the IndexedPiece, with the idea they correspond
to things that don't correspond to particular moments in a piece.
Moved indexer.py to "analyzers" Subdirectory, ...

And other significant changes.
Add __init__.py and experimenter.py in "analyzers" Subdirectory
Add Some Unit Tests for NoteRestIndexer
Add IndexedPiece and AggregatedPieces to models/__init__.py