cleaning up hierarchical consistency issues

[bmcfee]

In response to issue #13.

This PR implements the following:

• Z boundaries are now propagated to lowercase.txt ; this was done by modifying the parser script.
• inserting lower-case boundaries wherever there's an upper-case boundary. The notebook in the Not every boundary has a lowercase annotation #13 thread identified 171 files where this occurred. For now, I'm doing this manually by downcasing the uppers.

At some later point, #14 should replace Z boundaries with a must-have non-music tag.

I'll update the title of this PR once the smoke clears and it's ready for review.

[bmcfee]

Note about downcasing uppers: I'm only preserving the letter if it doesn't conflict with one already in use. Otherwise, I find a new unused letter.

The exception to this is when it's an obvious typo/mistake, and it's clear what the lower should be.

[bmcfee]

Hitting some strange edge cases here. For example, 765/textfile2 has lowercase annotations of the form d/b.

@jblsmith What should be done with these cases?

EDIT: it's only two files: 762/textfile2 and 775/textfile2.

[bmcfee]

quoting from previous thread:

And for non-standard letters, a standard could be: "assign ambiguous cases a new letter."

I've done this for the two tracks in question (765.2, 775.2). Everything now passes the alignment test and validates properly.