Fix issue #13 'Single-element arrays are not preserved'

[vyrp]

In Powershell, if a function returns an array of only one element, it gets unwrapped. This is the root cause of issue #13.

This Pull Request fixes it by correctly returning the array.

Simple example:

function F($l) { return $l }

$result = F(@("a", "b"))
$result                     # a
                            # b
$result.GetType().Name      # Object[]
$result[0].GetType().Name   # String

$result = F(@("a"))
$result                     # a
$result.GetType().Name      # String (Ouch!)

$result = F(@())
$result                     #
$result.GetType().Name      # ERROR! You cannot call a method on a null-valued expression.

function Better-F($l) { return ,$l }

$result = Better-F(@("a", "b"))
$result                     # a
                            # b
$result.GetType().Name      # Object[]
$result[0].GetType().Name   # String

$result = Better-F(@("a"))
$result                     # a
$result.GetType().Name      # Object[] (FIXED!)
$result[0].GetType().Name   # String

$result = Better-F(@())
$result                     #
$result.GetType().Name      # Object[]