Add a demo build for testing purposes

[kammce]

Each library will get a demo but the demos won't be something that the user can actually see change the outside world. The code will all be CPU based and in order to actually see changes the user will need to use a debugger and step through the code and its memory to verify that anything is happening.

These demos will need their own linker script and may only be usable on specific targets because the ROM and RAM locations could be anywhere in the address space.