Improve typings for typescript with generics

[msuntharesan]

This way, the store's state type and action type are inferred. This helps with autocomplete in editors.
Here is a sample of how it will be.

import * as React from 'react';
import { initStore, Store } from './dist';

type State = {
  count: number
}

type Actions = {
  increment: () => void,
  incrementBy: (by: number) => void;
}

const store: Store<State, Actions> = {
  initialState: { count: 0 },
  actions: {
    increment: ({ count }) => ({ count: count + 1 }),
    incrementBy: ({ count }, by: number) => ({ count: count + by })
  },
}

const { Provider, connect } = initStore(store)

type CountProps = { count?: number, actions?: Actions };
let Count: React.ComponentType<CountProps> = ({ count, actions }) => (
  <div>
    {count}
    <button onClick={actions.increment}>+</button>
    <button onClick={() => actions.incrementBy(3)}>+3</button>
  </div>
)

Count = connect(state => ({ count: state.count }))(Count)

const App = () => (
  <Provider>
    <Count />
  </Provider>
)

Type of the connect function can be improved though to accept incoming props and merge with props from selector function.

[coveralls]

Pull Request Test Coverage Report for Build 30

• 0 of 0 (NaN%) changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 28:	0.0%
Covered Lines:	40
Relevant Lines:	40

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💛 - Coveralls