fix(frontends/lean): wrong displayed type in proof with multiple sorry's, fixes #112

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(bin/linja): add copyright
feat(bin/linja): make deps when there are missing ones
feat(bin/linja): call lean after ninja if ninja failed
doc(emacs/README.md): clean up

[skip ci]
feat(bin/linja): linja calls lean if project does not exist

close #110
lean-mode checkpoint