[build] Change obj and bin output directory to toplevel
[build] Should enter from the parent directory -

otherwise XI_COMM_LAYER is not set the way you'd expect!
[build] Simplify how examples are organised -

* no need for subdirectories - it's not a app framework and
  should be kept simple, so a single example shall always be
  just one file

* adjust it to work the same way unit tests are done