Add note to jq.1 about shell quoting
Fix doc typos (.[foo] wanted to be .["foo"])
jv_invalid() shouldn't allocate

jv_invalid() should behave like jv_invalid_with_msg(jv_null()), and
neither should allocate memory, because neither ought to need to.
exec_stack.h was not using jv_mem_realloc()
Add jq_handle concept