Using DH, CE to accelerate
PEC as boundary done
PML mesh
change to sine source, FDTD source add 0.5Dt
PML complete

fix imperfact PML due to 0.5 Ds difference between positive PML and
negative PML
Merge branch 'master' of github.com:lc85301/FDTD

Conflicts:
	src/FDTD.cpp
	src/mesh.cpp
	src/mesh.h