refactored ex NOOP filter & specs into filter base specs

the NOOP filter is now a dynamically defined class into the `spec/filters/base_spec.rb` and the Plugin#lookup method has been adjusted to support dynamically defined plugins.
```
>> puts YAML.load("foo: |-\n  testing\n  fizz")
{"foo"=>"testing\nfizz"}

>> puts YAML.load("foo: |-\n  testing \n  fizz")
{"foo"=>"testing \nfizz"}
```