chore(emacs/lean-server): clean up debugging message
feat(emacs/lean-info): improve coercion display

close #124
fix(emacs/lean-info): print stale when info is available

fix #127
feat(frontends/lean/server): use alias (if available) in FINDG command output

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean): add '?' for inspecting the type of any expression, it produces a EXTRA_TYPE info entry

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>