Add string slicing
Test string slicing
Add slice builtin
Test slice builtin
Document string functions and slicing
Document string multiplication and division
Document split function
Add tojson and fromjson builtins
Test tojson and fromjson
Document tojson and fromjson builtins
Add -e | --exit-status CLI option
Document -e / --exit-status argument
Add -u / --unslurp opt for huge top-level arrays
Document -u / --unslurp option
Add ltrimstr and rtrimstr functions
Test ltrimstr and rtrimstr functions
Document ltrimstr and rtrimstr
Add callback interface for errors

Printing to stderr is not the right answer for a library.
Make length return abs value of numeric inputs
Add index strings by string; return string indexes

    % jq '.[","]'
    "a,bc,def,ghij,klmno"
    [1,4,8,13]
    %