fix(frontends/lean/parser): configuration options defined in a context are transient, fixes #162

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(frontends/lean/pp): pretty printing coercions to functions, fixes #151
feat(emacs/lean-company): "c-u TAB" asks filter for FINDG
fix(emacs/lean-company): color problem when showing auto-complete candidates
fix(emacs): use looking-at instead of char-after
dirty-buffer checkpoint