@dselsam @kha: The new class allows us to use `EState` even when part of
the state must be backtrackable. The default instance ensures that
there is no backtrackable state. The new test shows how to use it.
This is just a draft.
```
for f in `find . -name '*.lean'`; do echo $f; gsed "/^import/s/\b\(.\)/\u\1/g" $f > tmp; gsed "/^Import/s/Import/import/g" tmp > $f; done
```
