More fields in past_values for moves

Hey,
first of all, I am not sure if this is a bug or simply not implemented yet.

When looking at the data for moves, I saw that some move changes are not represented in the API.
If a move has changed behavior for stat changes or ailment chance, it still has a past_values entry but with nothing meaningful inside.

Examples:

1. Fire Blast:
   The move's burn chance has changed from 30% to 10% after gold-silver. There is a past_values entry for gold-silver, but the ailment_chance change is not shown. All other values inside the entry are null, so it would seem, nothing is changed at all.

2. String Shot:
   String Shot's status effect has changed since gen VI from speed -1 to speed -2. Here is also a past_values entry, but with no meaningful changes listed. The entry is for sun-moon instead of x-y, but that seems to be an issue with the veekun entry that is wrong.

So in summary there should also be fields for meta, stat_changes and effect_entries inside a past_values entry to also reflect changes that are not just power, accuracy, pp or type.
Maybe the effect_changes field was intended to be used for this purpose, but is currently always empty (at least in the few examples I have checked). However, it would be better to just list all the changes in the past_values entry anyway, imo.

Start by comparing the move endpoint data for Fire Blast and String Shot with their documented historical changes. Check how past_values currently represents power, accuracy, PP, and type, then determine how meta, stat_changes, and effect_entries should be represented; done means those historical changes are exposed meaningfully in the API.