Add SBC14

algorithms/math/legendre.cpp

algorithms/structure/disjoint_set.cpp

contests/SBC14/A.cpp

contests/SBC14/B.cpp

contests/SBC14/C.cpp

contests/SBC14/F.cpp

contests/SBC14/G.cpp

contests/SBC14/H.cpp

contests/SBC14/I.cpp

contests/SBC14/K.cpp