Fix problems with fetch

Make --destination optional. Only create destination directory if it doesn't exist.
Fix logging

Set log level according to command line. Make default level INFO. Add log statements for training.
Proper detection of command-line subparsers
Basic index and embedding
Simple Ngrams
Syntax for embedding lookup
Basic index and embedding
Merge branch 'feature/embedding' of github.com:wpm/Dorado into feature/embedding

Conflicts:
	dorado/embedding.py