Add metric learning facilities

[lebionick]

I have a task in which I need to match several texts with huge (~1M texts) database. Even though available models are pretty fast, this is not enough. The best way to tackle this problem is learning embeddings of texts and match them using Kd-tree etc. But as far as I understand, all models accept two texts and map them into class probs or rank value.

Is possible to somehow use matchzoo in the paradigm of metric learning already or will it be in the future?