TypeScript rewrite

[papb]

• Full TypeScript rewrite, except for the tests
  • We now have our own TypeScript typings, so no need for @types/umzug anymore
• Use XO as linter
• Use AVA for new tests
  • One day we shall move the old tests from mocha to AVA + TypeScript as well
• Remove Bluebird entirely
• Almost no breaking changes (the tests are almost the same!)
  • BREAKING: You now have to use const { Umzug } = require('umzug') instead of const Umzug = require('umzug') - this is probably the only truly relevant breaking change
  • Breaking: removed Bluebird so you can no longer use things like .tap directly on the Promise returned by some umzug method (you will have to wrap it first)
  • Breaking: renamed Storage to NoneStorage (I doubt anyone uses this though)
  • Breaking: removed the already deprecated old Umzug Storage constructor