add learn multiple metric with pegasos algorithm

1, modify the scalefeature scheme, first rescale each dim according to
the maxvalue of that dim, so for each dim, its range from [0,1], then
save alpha for each feature.
2, modify do_pr_evaluation, add more informative debug informations. now
there are 3 evaluation methods: vote scheme, distance scheme, global
scheme.
3, modify base_distance, now we use code from shaoting zhang,
GetL1/L2Dist
4, add some items in config file, such as feature type, feature
dimension, etc.