Pass arbitrary expressions as parameters.

This works:

    PASH> $x = 1 ; Write-Host $x
    1
`for` statements

This works:

    for ($i = 0; $i -ile 4; $i++) {Write-Host $i}

Some serious caveats are described in issue #102.
Merge pull request #103 from JayBazuzi/for

`for` statements