Merge current XBART master into heteroskedastic XBART branch.
Reason: intend to switch heteroskedastic code to a single State object and base it off of the current version of State object.
This should also simplify further merge of heteroskedastic code into master.
Merge current XBART master into heteroskedastic XBART branch. Reason: intend to switch heteroskedastic code to a single State object and base it off of the current version of State object.
This should also simplify further merge of heteroskedastic code into master.