fix Cmd::Subject::{Pg,Vg}

	modified:   lib/App/vaporcalc/Cmd/Subject/Help.pm
	renamed:    lib/App/vaporcalc/Cmd/Subject/PG.pm -> lib/App/vaporcalc/Cmd/Subject/Pg.pm
	renamed:    lib/App/vaporcalc/Cmd/Subject/VG.pm -> lib/App/vaporcalc/Cmd/Subject/Vg.pm