Use template literals for swipe direction callbacks

[stefvhuynh]

• Uses template literals for swipe call callbacks
• Upgrades to [email protected], which uses typescript@4

TODO before merge

• These changes have caused the package to exceed the size limit by 82 bytes. This could be due to the dependency update, so we should decide how to handle this (bump up the limit slightly or try to slim the bundle a bit).

[hartzis]

Closing PR for now. We'll try to tackle this in v7 but after we remove microbundle and use rollup.

• Replace microbundle with rollup #273