This option saves metadata sidecar (sdr) directories not next to the book or in koreader/docsettings/, but in koreader/hashdocsettings/ using the partial md5 hash of each documents, allowing users to move, rename, and copy their documents outside of KOReader without accidentally losing their highlights/notes/progress. Included are various warnings and info to users of the benefits and drawbacks of this non-default option.
Closes#10892.
```
08-12 14:32:17.325 9188 9216 E luajit-launcher: Failed to run script: frontend/util.lua:291: cannot open /storage/emulated/0/koreader/data/dict: No such file or directory
08-12 14:32:17.333 9188 9216 V threaded_app: android_app_destroy!
```
Currently only tested on Ubuntu-touch emulator with framework
ubuntu-sdk-14.10 for armhf.
The ubuntu-touch port is binary compatible with the Kobo port
major changes in this PR are:
1. rename the emulator device to sdl device since both the emulator
and the ubuntu-touch target use libsdl to handle input/output.
2. ubuntu-touch app has no write access to the installation dir so
all write-outs should be in a seperate dir definded in `datastorage`.
On kindle, kobo and pocketbook the data directory is the current
running directory but on Android the app is installed in system
defined location and users may have no access to that location.
The same circumstances should be true for the upcoming Koreader for
Ubuntu touch, so the data directory (in which tessdata, dictionaries,
global settings, persistant defaults and probably history data are
stored) could be stored in another place.
