Add :collapse to table DSL attribute rows
XML->SQL mapping in separate file
Experiment with VTD instead of Xalan for XPath
Fix measurements-table def
DSL: functions to define column value mappings

And more complete study import
Get rid of clj-xpath compatibility hacks
Refactor test to use DSL generator fn's
Remove intermediate vector format for DSL
Remove final uses of vector format
Move table definitions to separate file

Also, restrict studies query to namespace
Import xsd:duration as PGInterval
Fix arm_size to be integer
Import nearly all tables

 - re-enable enum types
 - import datetime
 - add table definitions
 - some refactoring of SQL schema
Refactor {xml-id sql-id} context format
Accumulate contexts stack in insert-table
resolve-fn in *-ref functions for stack traversal

 - The default `resolve-fn` is `first`
Import drug references in treatment activities

 - Using new "further up the stack" reference resolution
Import: add units, treatment-dosings, designs
Fix import of study start/end dates
Allow measurements on overall population (magic arm)