The airportinfo() and navinfo() functions in Nasal are second class citizens to their C++ counterparts, with Nasal used to prototype functionality in glass cockpits.
This patch provides a backward compatible extended function parameter list to allow greater access to apt.dat and nav.dat data.

1. The groundradar texture is centred on the tower position at a airport, add the tower position to the HashSet values returned.

2. Extends airportinfo() with optional parameters;
airportinfo([lat, lon], {type | id}, [range])

3. Extends navinfo() with optional parameters;
navinfo([lat, lon], {type [, range] | [frequency,] id})

Examples:
# find single airport by ICAO
var apt = airportinfo("YSSY");
debug.dump(apt);

# find single nearest airport
var aptNear = airportinfo("airport");
print("find nearest airport");
debug.dump(aptNear);

# find "vor" within 5.0nm of apt (YSSY)
var navList1 = navinfo(apt.lat, apt.lon, "vor", 5.0);
print("navList1 size: "~size(navList1));
debug.dump(navList1);

# find "ils" within 5.0nm of apt (YSSY)
var navList2 = navinfo(apt.lat, apt.lon, "ils", 5.0);
print("navList2 ils info");
debug.dump(navList2);

# find all navaids starting with 'HAM'
var navList3 = navinfo("HAM");
print("navList3 id 'HAM'");
debug.dump(navList3);

# find all "vor" within 5.0nm of current position
var navList4 = navinfo("vor", 5.0);
print("navList4 size: "~size(navList4));
debug.dump(navList4);

# find all "vor" starting with 'SY' ordered by distance from apt (YSSY)
var navList5 = navinfo(apt.lat, apt.lon, "vor", "SY");
print("navList5 size: "~size(navList5));
debug.dump(navList5);

# find all navaids with frequency 112.50 starting with 'SY'
var navList6 = navinfo(112.50, "SY");
print("navList6 size: "~size(navList6));
debug.dump(navList6);

# find all airports within 20nm of current position
var aptList1 = airportinfo("airport", 20.0);
print("aptList1 size: "~size(aptList1));
debug.dump(aptList1);

# find all airports within 20nm of Hamburg (index 2 of the VOR list starting with 'HAM')
var hLat = navList3[2].lat;
var hLon = navList3[2].lon;
var aptList2 = airportinfo(hLat, hLon, "airport", 20.0);
print("aptList2 near HAM size: "~size(aptList2));
debug.dump(aptList2);

# find all airports within 20nm of EGLL
var aptList3 = airportinfo("EGLL", 20.0);
print("all airports within 20nm of EGLL size: "~size(aptList3));
debug.dump(aptList3)