LiteralNER shall tokenize each entry

[jmansilla]

Right now our LiteralNER is very literal, so in some cases is not working.

Example: an entry like this

takayasu's arteritis

Is never found because the documents will be tokenized, transforming this

John had takayasu's arteritis

into this

John had takayasu 's arteritis

making impossible a match (notice that 's is a separated token).

Also, what make things harder is that the tokenizer to use while parsing the LiteralNER entries must be the same tokenizer used when tokenizing text.

[rafacarrascosa]

For documentation's sake,, something we talked in real life:

Perhaps tokenization, pos-tagging, ner-tagging and segmentation could be non-optional parts of the preprocessing pipeline since iepy's core would break without them anyway.

If those parts are non-optional, then they can be passed as kwargs to the preprocessing pipeline and therefore it can be easily ensured that tokenization is the same for both documents and literal tagging.