Proposal: allow state param to be object _or_ function

[jameslaneconkling]

Currently, state object type (POJO or Immutable.js collection or whathaveyou) can be configured by passing a third argument to the reducer function

combineReducers({
  ...reducers,
  ui: (state, action) => ui( state, action, Map )
})

And keys in the ui state tree can be either keys or functions in order that they can be initialized based on component props.

@ui({
  state: {
    uiVar1: '',
    uiVar2: (props, state) => state.router.location.query.searchTerm
  },
  ...
})

Proposal: allowing the entire state param to be either an object or a function could simplify the above two features, and result in fewer function calls when initializing the state.

E.g.

// state as plain object
@ui({
  state: {
    uiVar1: 'this',
    uiVar2: 'that'
  }
})

// state as function
@ui({
  state: (props, state) => ({
    uiVar1: 'this',
    uiVar2: state.router.location.query.searchTerm
  })
})

// state as function returning Immutable.js collection
@ui({
  state: (props, state) => Immutable.Map({
    uiVar1: 'this',
    uiVar2: state.router.location.query.searchTerm
  })
})

Any issues/cases I'm not covering here?

If you're interested in this extension to the API, I'd be happy to submit a PR.