Write a function named `flip_half`

that reverses the order of half of the elements of a `list`

of integers passed as a parameter.
Your function should reverse the order of all the elements in odd-numbered positions (position 1, 3, 5, etc.) assuming that the first value in the list has position 0.
For example, if the list originally stores this sequence of numbers when the function is called:

index: 0 1 2 3 4 5 6 7
[1, 8, 7, 2, 9, 18, 12, 0]

Then it should store the following values after the function finishes executing:

index: 0 1 2 3 4 5 6 7
[1, 0, 7, 18, 9, 2, 12, 8]

Notice that numbers in even positions (positions 0, 2, 4, 6) have not moved.
That sub-sequence of numbers is still: (`1`

, `7`

, `9`

, `12`

).
But notice that the numbers in odd positions (positions 1, 3, 5, 7) are now in reverse order relative to the original.
In other words, the original sub-sequence: (`8`

, `2`

, `18`

, `0`

) - has become: (`0`

, `18`

, `2`

, `8`

).

*Constraints:* You may use a single list as auxiliary storage.