fix(library/hott/Makefile): specify LEAN_OPTIONS "--hott"
fix(bin/lmake): fix typo LEAN_OPTIONS
feat(emacs/lean-flycheck.el): add lean-flycheck.el
feat(emacs/lean-settings.el): add customization-settings file
feat(emacs/lean-util.el): add lean-util.el
refactor(emacs/lean-mode.el): clean up, add license
feat(emacs/lean-mode.el): use whitespace-cleanup-mode to fci-mode
fix(bin/lmake): pass lmake option to makefile
feat(emacs/README.md): add README.md
feat(emacs/README.md): add instr. for MELPA; add whitespace-cleanup-mode
fix(emacs): use cl-case, require cl-lib
fix(library/standard): remove long comments introduced by b2c2d1d
feat(emacs): use optional package when required
feat(emacs/lean-setting.el): add lean-rule-color custom-var
feat(emacs): provide an option to disable lean-flycheck
feat(emacs): add lean-flycheck-turn-on/off/toggle
fix(library/unifier): make sure the imitation step is type correct, fix ensure_sufficient_args

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>