Support array input for terms in TrainingDocument

[nickmcblain]

When training my bot I want to be able to provide an array of terms to match to one skill. It is really awkward to create a TrainingDocument for every permutation of a search term when trying to match them to 1 skill. Allow for creating TrainingDocuments maybe?

[manthanhd]

@nickmcblain How are you picturing this to work?

[manthanhd]

@nickmcblain Something like this? https://github.com/manthanhd/talkify/pull/41