clog: make nil Logger safe (#436)
clog: make nil Logger safe (#436)

Also add documentation and license header.
deskr/cayley,cayleygraph/cayley,deskr/cayley,deskr/cayley,kortschak/cayley,cayleygraph/cayley,barakmich/cayley,deskr/cayley,kortschak/cayley,h4ck3rm1k3/cayley,barakmich/cayley,kortschak/cayley,pombredanne/cayley,kortschak/cayley,pombredanne/cayley,kortschak/cayley,h4ck3rm1k3/cayley,h4ck3rm1k3/cayley,pombredanne/cayley,barakmich/cayley,barakmich/cayley,h4ck3rm1k3/cayley,h4ck3rm1k3/cayley,pombredanne/cayley,barakmich/cayley,deskr/cayley