Website changes: add twitter handles and another disclaimer/beta signup link.
Include specific details for how to indicate missing values.
Link to VM download link instead of directly to VM
Fix export samples output message bug.
Merge branch 'master' of github.com:mit-probabilistic-computing-project/BayesDB
Support create models in parallel.
Merge branch 'master' into bql2

Conflicts:
	bayesdb/client.py
	bayesdb/engine.py