Adaptable enhancements

In using Adaptable classes usually we use only one configuration at a time, but we always have to pass the first parameter to specify the desired config. So I have a suggestion to make this task less tedious using the following API (along with the current API):
```
$cache = Cache::instance('default');
$cache->read('key');
$cache->write('key', 'value');
$cache->delete('key');
```
Current API:
```
Cache::read('default', 'key');
Cache::write('default', 'key', 'value');
Cache::delete('default', 'key');
```

This pull request is a proof of concept and if you agree, I will write docs and tests for it.