implement C++ version of sparse.model.matrix
debug: mistake of calling std::vector::resize
finish v0.1, directly expand the features
implement tag API for hashed.model.matrix2
implement keep_hashing_mapping
remove original hashed.model.matrix
update man
remove NOISY_DEBUG
type checking
make some function becomes template functions. Someday will try to implement a version for class(data) == "environment"
correct test for new API
correct C APi
update version
resolve #6
skip zero x for DenseConverter
implement hashed.model.matrix for NA
merge

Merge branch 'dev/hashed_model_matrix2' of github.com:wush978/FeatureHashing into dev/hashed_model_matrix2

Conflicts:
	src/hashed_model_matrix.cpp