refactor(emacs/lean-server): clean up
fix(emacs/lean-company): enable auto-complete if prefix has '.' or '_'
feat(emacs/lean-company): truncate type info in auto-complete

Close #137
feat(bin/ltags): resolve abbreviation('a') to definition

Close #131
feat(emacs/lean-tags): block emacs until ltags finishes
feat(emacs/lean-server): kill the server before emacs exit

Close #138
refactor(library/data/sigma): cleanup module