Support dumping OpenMW files in esmtool
For now esmtool
description says that it supports only "Morrowind ES files (ESM, ESP, ESS)" files, but not files from OpenMW (omwgame, omwaddon and omwsave), what it a quite strange.
Reading omw* files should be mostly fine, but esmtool expects that all files use the legacy encoding, while OpenMW's files (at least, omwsave ones) use the UTF-8.
So we need:
- Add a UTF-8 mode for esmtool (which will just do not set an encoder for EsmReader).
- Modify esmtool description.
Not sure how compare and clone modes are supposed to work.