move oc_codebook to folder
add sqldatamart files
add a couple of comments
pg8.4 compatibility changes
-concat replaced by dollar quoting and pipes
-string_agg replaced by subquery, array_to_string, array_agg
add item_name_hint for friendly column names
add subquery to:
-fix issue where columns created in wrong order
-make it easier to create and drop
added readme