Add more examples #39

Examples are located in the examples folder. The more examples, the better!
Everyone's contribution is welcome. If you have an interesting DAE system in mind, please feel free to post it here or create a new issue. You can also implement it in the code and create a Pull Request.

I am planning to add at least 3 more examples:

• A simple 3-equation system example that will demonstrate solution output options and setting up the specific output times
• Robertson DAE from the previous version of dae-cpp
• Two-body example from the previous version