Add dynamic evaluation to LSTM baseline

[larocheh]

This approach is described here:

https://arxiv.org/abs/1709.07432

In our setting, we would like consider 2 ways of doing dynamic evaluation

• Ignore the support set at evaluation time and only do dynamic evaluation when going over the query set
• Do a pass on the support set with dynamic evaluation, before doing dynamic evaluation on query set. However, we only report the NLL for the query set.