use the Preferences API for DictionarySettings

The preferences API provides a cross-platform persistence solution,
so no special logic is required for storing Windows settings files
anymore. This actually simplifies the preferences handling quite
a git.
read command line dictionaries in dictionary demo

The dictionary demo can better demonstrate functionality with larger
dictionaries. Therefore, if the user passes in a path to compiled
edict dictionaries, load those instead of the single entry demo
dictionary. Closes #7.
add demo-edict target to ItadakiDictionary

Add a build target to run the dictionary demo using the edict
dictionary. This is work for issue #9.
update README.md with build info for ItadakiDictionary

Add a section on compiling the dictionary tool and running the demo.
add note about usage of FastTextPane

The caveats of FastTextPane should be listed so that it is clear where
it will and will not be useful. Add a note about it only scrolling
by paragraphs.