Restructure ping_pong.lfe to better show callbacks/client API
Restructure ping_pong.lfe to better show callbacks/client API

rvirding/lfe,jjhoo/lfe,yurrriq/lfe,yurrriq/lfe,bsmr-erlang/lfe,jjl/lfe,lfe/lfe,lfe/lfe,arpunk/lfe,oubiwann/lfe,oubiwann/lfe,arpunk/lfe,bsmr-erlang/lfe,jjl/lfe,rvirding/lfe,jjhoo/lfe