Add new example file with core LFE macros.
Add new example file with core LFE macros.

This example file contains many of the core LFE macros written
in LFE. They are all include in lfe_macro.erl but here we show
how they could have been written in LFE.

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