Support dev install on windows

[squirrelsc]

1. Add scripts in install.ps1 to support install as devlopment.
2. Add nasui uninstall scripts in uninstall.ps1.
3. Use rmdir more, as it works with symbolic links better.
4. Simplify development document, and include this change in it.

[liuzhe-lz]

What's the drawback of Remove-Item?

[squirrelsc]

Remove-item doesn't work for symbol links. If use powershell to remove a symbol link, it needs to call like (Get-Item xxx).Delete(). But the Delete() doesn't work for non-empty physical folder.