Issue #110, formatting with empty parameter leaves delimiters intact

I had to downgrade the testproject from .NET v4.5 to v4.0 since I'm using Visual Studio 2010; all tests still pass. The reference i18n.Domain.Tests to i18n is required for `NuggetLocalizer.ConvertIdentifiersInMsgId`, should this method perhaps be moved to the i18n.Domain project instead?