fix(emacs/lean-option): handle lean-option-string when it's nil
feat(bin/linja): pass -D config option to lean

Close #196
feat(lean-option): handle default pp.width option value
test(emacs/lean-option-test): add lean-test-update-string-alist-default
test(emacs/lean-option-test): add lean-test-update-string-alist-default