feat(emacs/lean-server): scroll debug buffer
feat(emacs/README.md): add instruction for unicode font
feat(emacs/lean-server): add debug-mode, trace-mode
refactor(emacs/lean-server): restructure async queue handling routine
feat(emacs/lean-flycheck): delete flycheck temporaries after check

Close #140
feat(emacs/lean-flycheck): delete flycheck temporaries after check