Support negative rectangle coordinates (#12)

Since i3 4.22 now supports gaps, negative gaps can cause nodes
(workspaces, windows, ...) to have negative coordinates which we did not
support.

However, sometimes i3 reports negative coordinates as `uint32_t`.
Because of this the range of possible values for rectangle coordinates
are `[INT32_MIN, UINT32_MAX)`.
To work around this, we just read an int64_t.

Ref: i3/i3#5352
Ref: polybar/polybar#2888

include/i3ipc++/ipc.hpp

@@ -28,8 +28,8 @@ std::string  get_socketpath();
  * Primitive of rectangle
  */
 struct rect_t {
-	uint32_t  x; ///< Position on X axis
-	uint32_t  y; ///< Position on Y axis
+	int64_t  x; ///< Position on X axis
+	int64_t  y; ///< Position on Y axis
 	uint32_t  width; ///< Width of rectangle
 	uint32_t  height; ///< Height of rectangle
 };

src/ipc.cpp

@@ -44,8 +44,8 @@ std::vector<std::ostream*>  g_logging_err_outs = {
 
 inline rect_t  parse_rect_from_json(const Json::Value&  value) {
 	rect_t r{};
-	r.x = value["x"].asUInt();
-	r.y = value["y"].asUInt();
+	r.x = value["x"].asInt64();
+	r.y = value["y"].asInt64();
 	r.width = value["width"].asUInt();
 	r.height = value["height"].asUInt();
 	return r;