Econ81500: homeworks / lecture notes

reorganized the files according to the topic. The last lecture is (partially) split into lecnotes8 and 9. (5/15/11)

lecnotes_Mar.3&10&24: titles on the front page corrected (4/15/11)

lecnotes_Mar.3&10: date on the front page corrected (3/26/11)

lecnotes_Feb.10 : date on the front page corrected (2/13/11)

lecnotes_Feb.3 : Some abuse of notation regarding the habit persistence (C, c) is now corrected.