changed directory layout to have src split into lib and app. Anything that will be compiled to a .a file goes in lib, anything compiled to an executable will go in app (i think this should just be barista_core and espresso_core). Created a top-level Makefile that recursively calls make on libraries and apps in their dependency order. Modified espresso_core to call the espresso main loop function that accepts rpc calls from the barista node.