* removed FLOOR_VECNAME_N macro, can use vector# type directly now
 * replaced most uses of FLOOR_VECNAME with vector_type, a new vector#<scalar_type> typedef
 * minmax_element and minmax_element_index are now only usable with vectors of width 2, 3 and 4 (dependency issue with width 1 + doesn't make much sense anyways)
 * renamed signed_vector typedef to signed_vector_type