Adding Embedding methods to crayon.py

[Spandan-Madan]

Currently there are only scalar and histogram methods. It would be AWESOME to have embedding methods, as that let's people like me who use PyTorch for unsupervised learning make use of Crayon.

If you think about it, Embedding is the most powerful tool on Tensorboard. Histograms and running averages (scalars) aren't hard to implement. PCA/TSNE interactively are not super easy.

Would be happy to work with other devs on adding embedding functionality if anyone's up! Any leads on how I should approach?