Directional skipgram
This release has the following changes:
- Add support for the directional skip-gram model (Song et al., 2018).
- Store norms in a finalfusion chunk, making it possible to retrieve the unnormalized embeddings.
- Better defaults in for skip-gram models: context size 5 -> 10, dimensions 100 -> 300, epochs: 5 -> 15
- Improved command-line option handling.