Fixed failing installation for clients with absolute binPath set.

Without this fix, it tries to install to `C:\C:\Commom\bin\ruby187` on my machine.
Added $binRoot = Get-BinRoot in comments - should be merged again before use.
Get-BinRoot.ps1 included while Chocolatey makes it to mainline.
Removing code and linking to included Get-BinRoot.ps1
Merge pull request #110 from Redsandro/patch-1

Fixed failing installation for clients with absolute binPath set.