* Revert changes to priority of `token_match` so that it has priority
over all other tokenizer patterns
* Add lookahead and potentially slow lookbehind back to the default URL
pattern
* Expand character classes in URL pattern to improve matching around
lookaheads and lookbehinds related to #4882
* Revert changes to Hungarian tokenizer
* Revert (xfail) several URL tests to their status before #4374
* Update `tokenizer.explain()` and docs accordingly
* avoid changing original config
* fix elif structure, batch with just int crashes otherwise
* tok2vec example with doc2feats, encode and embed architectures
* further clean up MultiHashEmbed
* further generalize Tok2Vec to work with extract-embed-encode parts
* avoid initializing the charembed layer with Docs (for now ?)
* small fixes for bilstm config (still does not run)
* rename to core layer
* move new configs
* walk model to set nI instead of using core ref
* fix senter overfitting test to be more similar to the training data (avoid flakey behaviour)
* merge_entities sets the vector in the vocab for the merged token
* add unit test
* import unicode_literals
* move code to _merge function
* only set vector if vocab has non-zero vectors
* Update sentence recognizer
* rename `sentrec` to `senter`
* use `spacy.HashEmbedCNN.v1` by default
* update to follow `Tagger` modifications
* remove component methods that can be inherited from `Tagger`
* add simple initialization and overfitting pipeline tests
* Update serialization test for senter
* Improve token head verification
Improve the verification for valid token heads when heads are set:
* in `Token.head`: heads come from the same document
* in `Doc.from_array()`: head indices are within the bounds of the
document
* Improve error message
* Fix model-final/model-best meta
* include speed and accuracy from final iteration
* combine with speeds from base model if necessary
* Include token_acc metric for all components
