Provide a convenient interface for defining tagged print handlers for custom
types. All `register-...` functions take the same arguments: `[type tag to-edn]`

- `type` the type this handler is for (`java.lang.Class` or JS constructor)
- `tag` the symbol used as tag, without the `#`
- `to-edn` a function which takes the object to be printed, and returns plain
  data (vectors, maps, etc)

Create write handlers for Transit

The handlers simply get added to an atom, it's up to you to refer to them
when constructing your transit writer.