refactor(library/data/list): cleanup, rename concat to assoc
fix(frontends/lean/parser): segmentation fault after REPLACE, fixes #172
feat(emacs/lean-server): print out signal event to debug buffer
chore(.travis): install valgrind before we install c++ compiler
feat(emacs/lean-server): handle modified buffer when send VISIT cmd

Close #159
fix(emacs/lean-server): respect order of messages in check-buffer-and-partition
start a new project checkpoint