.gitmodules: add .elisp/git-modes
.zshrc: experiment with l = g s in worktree

We always have the escape hatch ls.
.emacs: replace commit-mode with git-modes

The commit-mode branch I prepared for magit is now abandoned.
.gitmodules, .emacs: swap out eltbus for zenburn
.gitconfig: alias rp = rev-parse
.zshrc: use the output of g rp --is-inside-work-tree
.zshrc: discard output of cd -