Nested keys example for Readme 

To show usefulness of validating a single object with nested keys rather than lots of individual vars
```
<input type="text" name="address.town">
...
<input type="text" name="address.postalcode">
```
Then the rules:
```
getRules(){ 
   const result = { 
   ['address.town'](val) { 
   ... return valid
   }
  ['address.postalcode'](val) { 
   ... return valid
}
```
