Moved the to_mat3() method in qtn4.cpp to qtn4_to_mat3() function in utility.hpp
Moved constructors qtn4(vec3) and qtn4(vec3, float) to vec3_to_qtn4 and vec4_to_qtn4 in utility.hpp
Moved norm_sqr(), norm(), normalized() and normalize() in qtn4 to utility.hpp