lua api : remove unused functions
lua : update internal copy to 5.2.3
Add function to load xmp for a single image
Simpler function to append version for duplicates
Write to correct xmp file when manually writing

this was broken for duplicates
Bump db version to 2: write_timestamp
Update write_timestamp when writing xmp file
Add a crawler that checks all xmp files on start
lua : api, enable external formating functions

this should solve most of the problems of wiki vs usermanual syntax
lua : always expand path name before importing a directory
change dt_film_cleanup to not always destroy empty films.

lua needs to create empty films
lua : add a function to create an empty film

dt.films.new("directory"):dt_lua_film_t
Fix typo in preference defintion.