added confidence changes to docs
added new conf parsing. Not handled yet by engine or blocked in select and simulate
added checks for conf in simulate and select
Merge branch 'dev' of https://github.com/mit-probabilistic-computing-project/BayesDB into confidence-refactor
update help
Fix help messages
Massive massive refactoring of SELECT and INFER.

Individual confidences are now supported in INFER queries with 'conf', e.g.
INFER a conf 0.4, b conf 0.7, c FROM table.

Where clause confidences are now supported for all where clause operators.

Huge speedup/refactoring in the order of function evaluations:
now, functions (including imputations) are only evaluated when necessary,
and are never computed more than once per query (e.g. if in the query clause,
where clause, and order by clause, the same value will be used for all).
Merge branch 'confidence-refactor'
Merge branch 'master' of github.com:mit-probabilistic-computing-project/BayesDB