Track appropriate events when this plugin makes changes

[simonw]

Datasette has an events system as of 1.0a8: https://docs.datasette.io/en/latest/events.html

This plugins should trigger the following events at various points, if it is running under Datasette 1.0a8 or higher:

• create-table
• drop-table

Refs:

• track_event() mechanism for analytics datasette#2240

Can't track alter-table until the following issue is shipped in a release:

• Alter table support for the JSON write API datasette#2101

Hence this follow-on issue:

• Track AlterTableEvent once it is in a Datasette release #54