WIP-MEI: Formatting: Minor Style Corrections
WIP-MEI: WIP on Importing <staff> and <measure> Tags (TOTAL WIP)
Revert "WIP-MEI: New: _filterNamespace() Function to Avoid URI-Prefixed Tag Names"

This reverts commit 9005de0b43146aa856c3a0b1bbf5313c4d746447.

CRA: Changed my mind! We'll just go with the full namespace for now...
WIP-MEI: moving toward full-namespace tag names
WIP-MEI: Moving Exception Text to Module Constants

Collected at the top of the file, this allows re-use and easier review and
translating. Hopefully this will encourage easier-to-understand error messages.
WIP-MEI: Added note clarifying non-use of namespaced tags in tests

These functions assume they have the correct tag. The tag name we use
for testing is therefore irrelevant.
WIP-MEI: Change @xml:id to Use a Full-Namespace, Module-Level Constant

This is how ElementTree will import the @xml.id attribute, so it's how
we need to find it.
WIP-MEI: New: mei.allPartsPresent() Function to Deduplicate <staffDef> Tags

We'll need to know the unique @n values for every <staffDef>. This allows us to
iterate through the <measure> tags and predict what @n values we might see, so
we can build a stream.Part incrementally.
Release version v1.9.3.
Release version v.1.9.3
Merge branch 'master' into mei
WIP-MEI: Fixed: Rewrote layerFromElement() (for <layer> ==> Voice)

The function now follows our requirements carefully. There are also unit
and integration tests.

(This function first appeared in bb8fdf52a2033854ba3c265e1b6ec957927d14fa)
WIP-MEI: New: staffFromElement() converts <staff> tags to a list of Voice

You might think it would convert to a Part, but you would be wrong!