scale-generator: Remove inaccuracies in information provided

[guygastineau]

I noticed while reviewing a PR for this exercise to the bash track that there are some errors (I am a music composition major).

I believe that as a learning platform (even if not for music) that it is important for our exercises to involve accurate information.

I am willing to make a PR to the scale-generator exercise. This issue is to get the discussion started about the changes, and to act as a placeholder.

Here is the canonical-data.json

1. ~~We only need the interval specification up to the last scale degree before the octave. The interval distance from the {LT, subtonic, (sub-mediant in pentatonic or unrotated hexatonic)} to the octave is the inversion of distance from tonic to that note. Ie. A to G is a minor 7, thus G to A is a major 2. This is however irrelevant, because this exercise does not expect the octave to be printed, so the specification of intervals should be one less than the number of total notes printed.~~ I realized today teaching a friend interval inversion that I was wrong about this point. It is redundant, but the convention includes the final interval to the octave. Thus the specifications of intervals is already the correct number in these exercises. The other points remain unaffected by this.
2. A harmonic minor scale cannot have the flat version of the tonic as the LT (leading tone, the note a half step below the tonic). Therefore a D harmonic minor scale must have C# as the leading tone. Db would be used for a different type of chromaticism. I understand that this 'mixing' of sharps and flats would likely require additional work for the example exercises in each track. I would like to get feedback on everyone's willingness for this change. It would make the difficulty rating of the exercise spike in most tracks I presume.
3. The hexatonic scale test is actually what is called a whole-tone scale. specifically it is WT-1 in pitch set theory when built off of C#/Db. The hexatonic scale is a synthetic scale generated by alternating between half-steps and augmented seconds. I will correct the name of the existing test in the coming PR, and I will add a test for an actual hexatonic scale.

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I will look over the canonical-data.json to see if there are more problems.

I also would love feedback from the community regarding willingness to put up with this exercise at a much harder difficulty. with the modes, diatonic major, and natural minor it is true that there will never be sharps and flats mixed; however, when dealing with the melodic and harmonic minor scales there will often be flats and sharps in the same scale in order for the scale degrees to be named correctly.