Enhance Template Usage

[pjcast]

Hi,

I've briefly tested the changes, feel free to incorporate them. Some issues I encountered using your fork were:

• Couldn't use a custom reducer method
  • Had to update reducer template definition
• Dispatch to custom reducer actions wasn't possible
  • Updated template logic (borrowed from React)
• useStore forced to return whole type
  • Created an alternate method 'pickStore'. Uses Pick template. There are two ways one could use this in code:

const { user } = pickStore((store: StoreItems) => { return { 
    user: store.user,
    something: store.something
}});

Or:

const { user, something } = pickStore<'user'|'something'>();

I don't like using strings... but, it is using keyof, so, the strings have to be actual property methods... so, refactoring store item names would cause an error in either case.