Preparation for new unifier.
@dselsam: I had to make minor changes at `Synth.Lean`, and add messy
code to `Context.lean`. `Context.lean` will be deleted in the future.
So, it is not a big deal.
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
```
