hjq: cleanup Zip2F
hjq: improve `atF` (error messages, double as index, null)
hjq: add support for select()
hjq: use attoparsec-expr to greatly improve the support for binary operators
hjq: add the notion of Filter1
hjq: hide Ordering constructors
hjq: proper semantics for (,) and binay operators
hjq: better semantics for object building
hjq: cleanup dead code (binOpF)
hjq: comment
hjq: ignore -c
hjq: rename type into kind
hjq: better parsing, more operators...