Add mmap_mode="c" to np.load() of .npy files in embedding.py

[okayzed]

using mode "c" means copy-on-write, so the files are loaded off disk using mmap but not re-written to disk when changed.

• with cold file cache, running example.py takes ~4s vs 2.7s
• with hot cache, example.py takes 2.8s vs 1.8s

(for testing, i clear the fs cache using vmtouch tool: https://hoytech.com/vmtouch/)

[okayzed]

this may be a premature optimization, but since i've been running the program over and over, it's useful to me (and not changing results yet). thought i'd share it

[okayzed]

please disregard that last commit (with tsne viz) - i didn't realize it automatically would update this pull request with new commits. this pull request only contains one diff related to mmap

[williamleif]

Seems like a perfectly reasonably optimization! Thanks!