jeffreys distribution

here are the .C and .h files for the jeffreys distribution (JointPdf, VectorRealizer, VectorRV)
Yep :)  we'll have to add them.  Look at [`src/Makefile.am`](https://github.com/libqueso/queso/blob/dev/src/Makefile.am#L165) to see how we add source files to the build system.  Headers are a little more fiddly.  You still add them to the build system like source files (see the same file I linked), but you also have to execute:

```bash
$ cd inc/queso
$ ./rebuild_makefile.sh
```

Let me know if you have problems.