Topic/plat 6640 part3

This just adds demos for caplet stripping. These use the test framework (for conveniences) but are not tests as such. There is one class, `CombinedCapletStrippingResults`, which used purely as a helper class for these demos, which is not independently tested.  
When run these demos produce a lot of formatted numbers that can be pasted into Excel (or elsewhere) to produce plots. In particular, they are used to produce plots in the caplet stripping white paper I am writing. 
After discussion, the following has been agreed. Maven has no clean way to include "demo" code within the same project as the main code. The Maven Way promotes use of a separate maven project for this, however that is a non-ideal solution in this case, where there is a relationship between the tests and the demo code.

An attempt was made to add a folder "src/demo/java" but although it is possible with maven, it is not easy and causes problems with IDEs.

As such, the original proposal stands. Demo code must
* have a package name where the last segment is "demo"
* have class names ending in "Demo"
* may be main methods or tests using an annotation
* if tests then they should not have a test group
* a description may be added to the test annotation for clarity in PRs

The last point is designed to encourage code like this:

```
@Test(description = "Demo to generate foo-bar upside-down numbers")
public void test() {
```
Writing comments like this is encouraged to aid reviewers and as a reminder of what the code is for.