Vw helpers

## `vw_helpers` module
* parsers for standard vw output
* `LDAResults` object for working with results of `vw --lda` runs

## `SFileFilter`
Like a gensim dictionary but made for filtering sparse files for feeding into `vw`

## Updates
* `VWFormatter` object now works faster and passes tests
* `common.smart_open` allows using context manager
* `common.SaveLoad` is an ABC that facilitates [un]pickling

## tests
* Added `test/
* In, `test_declass`, tests of `vw_helpers`, `TokenizerBasic`, and