WordSieve class for working with all languages through a single object

Added a **WordSieve** class which could be used with all defined languages
```ruby
sieve = Stopwords::Snowball::WordSieve.new

filtered = sieve.filter lang: :en, words: ['has', 'cats']
# filtered = ['cats']

sieve.stopword? lang: :en, word: 'some'
# true
```