Change the common-sense check clause to catch exception, warn and drop

[serenalotreck]

After trying this on some real data, it looks like mismatching tokenizations of the entity annotations and source documents are somewhat common, so having the script error out wasn't ideal. I've added a try/except clause to catch the error and warn the user, and then a continue to skip the rest of adding the entity.

[dwadden]

Ah, the joys of tokenization. Sure, makes sense.

Two little suggestions:

• This might be a good place for a warnings.warn - see the warnings module - rather than a try/catch. That way, the user has control over how many warnings they want to see.
• You could also keep track of the total number of successful and failed matches as an attribute on the AnnotatedDoc class, and at the end of preprocessing print a message like {n_failed} / {n_total} entities were not matched successfully.

[serenalotreck]

Thanks for the feedback, I made those changes! It does print the {n_failed} / {n_total} after each individual doc, let me know if you'd like me to change that to do a total at the end of all docs.

[dwadden]

Merged.