Add JsonArray::skip_value for ignoring values when iterating.
Allow raw json data to be extracted from JsonObjects and JsonArrays.
Add empty() method to JsonArray to check if empty.
Tidy some comments.
Add methods to JsonObject to non-fatally set values by reference.
Change JsonDeserializer to take JsonIn, not always JsonObject.
Mark some info getter methods const.
Add constructor for empty JsonObject.

Conflicts:
	json.cpp
Add size() empty() and get_raw() methods to JsonObject.
Add read_into() methods to JsonArray.
Add empty virtual destructor to Json(De/S)erializer.
Add JsonObject::read_into templates for sets and vectors.
Return empty object from JsonObject::get_object if nothing found.
Tidy json.h a little.

Conflicts:
	json.h
point json autoserialization.
bionic json autoserialization.
Remove unused picojson.h and picojson error checking before game init.
Fix cursesport.cpp includes.
Megaconvert save system from picojson.h to json.h.

Conflicts:
	gamesave.cpp
	item.h
	player.h
	savegame_json.cpp
Only read_into vector/set elements if element successfully read.