helperfunctions to common Slice operations

[Esonhugh]

This PR is about following example.

E.g.

len(split("https://www.example.com/", ".", -1)) != 3 
// true, the len has toString() make the []string => string first and wrap it with [ and ] and make calc the len => 25

E.g.

(split("https://www.example.com/", '.',-1))[1] == 'example' 
// It has no such expression [n] to get the index[n] string
// and also this expression is not return bool. It make result as []string 

[Esonhugh]

@tarunKoyalwar

[tarunKoyalwar]

lgtm !

[Esonhugh]

Great bounds checking

lgtm !

[Mzack9999]

lgtm!