add parsing for unary + -
simplify the error position code
add casts, disable failing tests temporarily
add support for subqueries in scalar expressions
add support for in list, and fix code for in query expr
add support for between
split the Op ctor into binop,prefixop, postfixop and specialop
add support for is null
add support for more is ... postfix ops
add support for a bunch of keyword binary operators
tidyups
implement extract
add support for extended aggregate syntax
add window functions (without frames
add support for union,intersect,except
add support for union all and union corresponding and for intersect and except
few small fixes

untested fix for case insensitive keywords
add partial support for interval literals
fix bug in prefix operator cast parsing
work on parsing tpch

add parse function for parsing multiple query expressions separated by
  semicolon
add parser for substring operator
tweak the layout for pretty printing binary operators
add sql file with tpch queries in it
add simple exe to parse and pretty print multiple query expressions
add support for full table aliases
add with expressions, all tpch appear to parse correct, some of the later ones pretty print badly though
update todo