Add vector2 lua API for 2D vectors

.luacheckrc

@@ -15,6 +15,7 @@ read_globals = {
 	"dump", "dump2",
 	"fgettext", "fgettext_ne",
 	"vector",
+	"vector2",
 	"VoxelArea",
 	"VoxelManip",
 	"profiler",
@@ -24,7 +25,7 @@ read_globals = {
 
 	string = {fields = {"split", "trim"}},
 	table  = {fields = {"copy", "copy_with_metatables", "getn", "indexof", "keyof", "insert_all", "shuffle"}},
-	math   = {fields = {"hypot", "round", "isfinite"}},
+	math   = {fields = {"hypot", "round", "isfinite", "sign"}},
 }
 
 globals = {
@@ -71,6 +72,10 @@ files["builtin/common/vector.lua"] = {
 	globals = { "vector", "math" },
 }
 
+files["builtin/common/vector2.lua"] = {
+	globals = { "vector2", "math" },
+}
+
 files["builtin/game/voxelarea.lua"] = {
 	globals = { "VoxelArea" },
 }