Fixed issue #8. Segmentation fault when using the __repr__ method

This reverts commit ad5c67e4.

Added ONE_CLASS support

It seems that just checking if the file is good to read is not enough (std::ifstream::good).
This function reads one extra line.

I did a hard check with the number of samples and solved the problem.

Created and binded a method to read the number of support vectors per class. Also added unit tests for that