Version 2 - Now with hooks

A few updates to the library:

• Introduced useSequencer as the primary api for usage.
  useSequencer behaves functionally equivalent to the previous withSequencer higher order component, just translated for the world of hooks. withSequencer can still be used but it is deprecated.

• Better typings: Your step names now come up as string literal types in typescript, making sure you don't make a mistake with mistyping the names in your code.