Allow onCompile callback to be defined in config
Allow onCompile callback to be defined in config

Resolves #747

PeterDaveHello/brunch,hayesgm/brunch,hellyeahllc/brunch,lalomartins/brunch,justinwoo/brunch,Flaise/brunch,kidaa/brunch,ondreian/brunch,rlugojr/brunch,brunch/brunch