Post splat variables from MultipleAssignment should be scanned backwards.

This commit fixes the following scenario:

*a, b, c, d = [1, 2, 3, 4, 5]

Before:
[a, b, c, d] => [[1, 2], 5, 4, 3]

The generated bytecode pops from the array's tail and variables are assigned
in this order: b, c, d.

After:
[a, b, c, d] => [[1, 2], 3, 4, 5]

The generated bytecode pops from the array's tail and variables are assigned
in the correct (backwards) order: d, c, b.
Merge pull request #2 from razielgn/fix-splat-with-post-variables

Post splat variables from MultipleAssignment should be scanned backwards.