RapGenius is a nice site for viewing lyrics and understanding obscure (to you) references. But a tally sheet of line-by-line references is not really an "explanation" of a rap/song/poem. Literary allusion has a long history and it can deepen the intellectual/emotional experience of a work, but people can get too obsessed with understanding "references" while missing the forest from the trees.

It's great the site isn't limited to rap, though. No one has tackled explaining Howl yet :) http://rapgenius.com/Alan-ginsberg-howl-lyrics