fix(frontends/lean/server): '[anonymous]' entry being displayed by FINDP

This could happen when there is a declaration (e.g., nat) whose type is
equal to an active namespace.
fix(frontends/lean/parser): commit_upto invocation after 'import'
fix(frontends/lean/info_manager): bug in save_environment_options,
server was displaying old results
refactor(library/data/num): add 'succ', 'pred' and 'size' (aka number of bits),
rename is_inhabited theorems
test(tests/lean/interactive): test for issue #193
feat(emacs/lean-debug): add lean-debug minor-mode

close #177