Adds the .opensdf extension to git ignore.

The .opensdf and .sdf files are SQL Compact databases that contain the
Intellisense files for C++ that are built by Visual Studio. They can be
safely ignored and will be rebuilt when the project is opened.

They are not checked in to source control.
Adds the Static Library Reference Sample

This Visual C++ project demonstrates the declaration of a dll and
subsequent referencing and consumption of that dll. This technique will
allow common code to be separated into libraries.