Add merge strategy option support
Add merge strategy option support

perlpunk/git-subrepo,brijendratiwari/git-subrepo,ingydotnet/git-subrepo,dzzh/git-subrepo,perlpunk/git-subrepo,stsquared99/git-subrepo,dzzh/git-subrepo,ingydotnet/git-subrepo,brijendratiwari/git-subrepo,stsquared99/git-subrepo