add serialization to Gvec class
add serialization to Gvec class

electronic-structure/sirius,electronic-structure/sirius,toxa81/sirius,electronic-structure/sirius,toxa81/sirius,toxa81/sirius,electronic-structure/sirius,toxa81/sirius,electronic-structure/sirius,electronic-structure/sirius,toxa81/sirius,electronic-structure/sirius,toxa81/sirius