Upgrade to Ava 1.0

[sirtimbly]

https://blog.sindresorhus.com/ava-1-0-861d780b2d81

TypeScript support from this recipe? https://github.com/avajs/ava/blob/master/docs/recipes/typescript.md

This should greatly simplify testing scripts but might slow the tests down because of the loss of compileEnhancements ?