Added documentation for metadata statements to bql.rst
Added documentation for metadata statements to bql.rst

JDReutt/BayesDB,poppingtonic/BayesDB,poppingtonic/BayesDB,poppingtonic/BayesDB,JDReutt/BayesDB,JDReutt/BayesDB,poppingtonic/BayesDB,JDReutt/BayesDB,poppingtonic/BayesDB,JDReutt/BayesDB