MyRPL add operator

[+] can be used with lists and strings


Examples: 

(The meaning of -> is "see result at stack first level")

"abcde" ENTER "f" + -> "abcdef"
"z" ENTER "abcde" + -> "zabcde"
"abc" ENTER "DEFG" + -> "abcDEFG"

{ a b c d e } ENTER { f } + -> {a b c d e f} 
{ a b c d e } ENTER 4 + -> {a b c d e 4}
100 ENTER { A B } + -> {100 A B}

{ A B C D } ENTER {x y z} + -> {A B C D x y z}