Allow for multi-line class definitions in class_list.cpp.py

[jonpsy]

Currently, our class_list.cpp.py seems to be very sensitive to spaces and new line chars, this causes potential mess-ups when class names tend to get bigger. An immediate example would be
class RandomFourierGaussPreproc: public RandomMixin<DensePreprocessor<float64_t>> , doing a clang-format does

	class RandomFourierGaussPreproc
	    : public RandomMixin<DensePreprocessor<float64_t>>
	{

our python code fails to register this class on class_list.cpp.

[karlnapf]

thanks for reporting, I have noticed this a few times before as well

[karlnapf]

Context: class_list.py parses the C++ code to extract all class names used in the shogun codebase. We use this in factories to allow creating instances by name.