Feature/predefined normalization

fix #67 and [jubatus#255](https://github.com/jubatus/jubatus/issues/255)

I implemented 3 normalization `num_filter`
- linear scale normalization(o to 1 with/without truncate)
- gaussian normalization(-1 to 1 normalization)
- sigmoid normalization(0 to 1)

In this case, the variable `variance' should be `standard_deviation' or `stddev' as ordinary notations in statistics. To avoid confusing users, we should also change the name in params.
http://en.wikipedia.org/wiki/Standard_score#Calculation_from_raw_score