[emacs] assimilate lean-mode and dependencies

lib/async                master                    v1.9.3-1-g04e1a2c
lib/company              master                     0.9.6-23-gd26ec71
lib/f                    master                    v0.20.0
lib/flycheck             master                     31-118-g0c4bbd1f
lib/helm                 master                    v2.9.2-24-g56039aaf
lib/lean-mode            master                    6ed7031
lib/popup                master                    v0.5.3-20-g80829dd
lib/s                    master                     1.12.0-10-g03410e6