WISH: add /skip refinement to insert

[luce80]

add /skip refinement to insert so I can do:

>> head insert/skip [a b c] [1 2 3] 1 ; like a "zip" function
== [1 a 2 b 3 c]
>> head insert/dup/skip next [a b c] '_ 2 1 ; like a "chain" AKA "combine" function
== [a _ b _ c]
>> head insert/dup/skip next "abc" " , " 2 1
== "a , b , c"
;or ?
== "ab,,c"

This makes the function more "polymorhic" .