This patch implements lazy loading of the JSON data.
Motivation: in most requests not all JSON data is needed, but loaded. By
example these four JSON files:
- currencies.json ~550KB
- engine_descriptions.json ~1,3MB
- external_bangs.json ~1,3MB
- osm_keys_tags.json ~ 2,2MB
most often not used and consume a lot of memory and BTW they also extend the
time required to instantiate a walker.
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>
