Thesis code first commit
add functions target2tri and convert_target

target2tri maps amazon review rating output (1-5) to [0,1,2) (pos,neg,neut)  1,2 - neg, 3 - neut, 4,5 -pos

 convert_target takes a list with strings pos, neut, neg and converts to integers 0,1,2 for use with classification methods