* Fix most_similar for vectors with unused rows
Address issues related to the unused rows in the vector table and
`most_similar`:
* Update `most_similar()` to search only through rows that are in use
according to `key2row`.
* Raise an error when `most_similar(n=n)` is larger than the number of
vectors in the table.
* Set and restore `_unset` correctly when vectors are added or
deserialized so that new vectors are added in the correct row.
* Set data and keys to the same length in `Vocab.prune_vectors()` to
avoid spurious entries in `key2row`.
* Fix regression test using `most_similar`
Co-authored-by: Matthew Honnibal <honnibal+gh@gmail.com>
* Implement new API for {Phrase}Matcher.add (backwards-compatible)
* Update docs
* Also update DependencyMatcher.add
* Update internals
* Rewrite tests to use new API
* Add basic check for common mistake
Raise error with suggestion if user likely passed in a pattern instead of a list of patterns
* Fix typo [ci skip]
