Places an element at a specific index of an array:
```
_array = [1,2,3];
_index = 0;
_value = 0;
_array insert [_index, _value]; //[0,1,2,3];
_index = 3;
_value = 2.5;
_array insert [_index, _value]; //[0,1,2,2.5,3]
```
or maybe it could work like `append`:
```
_array = [];
_index = [0];
_values = [1,2,3];
_array insert [_index, _values];//[1,2,3];
```
alternative name: `insertAt`
maybe the command could support strings too?