Add Graph Illustrations to Doc

(cherry picked from commit 9ea619c486235d36fc8955669ddc93694605538c)

doc/classes/Node2D.xml

@@ -23,6 +23,7 @@
 			<argument index="0" name="point" type="Vector2" />
 			<description>
 				Returns the angle between the node and the [code]point[/code] in radians.
+				[url=https://raw.githubusercontent.com/godotengine/godot-docs/master/img/node2d_get_angle_to.png]Illustration of the returned angle.[/url]
 			</description>
 		</method>
 		<method name="get_relative_transform_to_parent" qualifiers="const">

doc/classes/Vector2.xml

@@ -35,6 +35,7 @@
 			<description>
 				Returns this vector's angle with respect to the positive X axis, or [code](1, 0)[/code] vector, in radians.
 				For example, [code]Vector2.RIGHT.angle()[/code] will return zero, [code]Vector2.DOWN.angle()[/code] will return [code]PI / 2[/code] (a quarter turn, or 90 degrees), and [code]Vector2(1, -1).angle()[/code] will return [code]-PI / 4[/code] (a negative eighth turn, or -45 degrees).
+				[url=https://raw.githubusercontent.com/godotengine/godot-docs/master/img/vector2_angle.png]Illustration of the returned angle.[/url]
 				Equivalent to the result of [method @GDScript.atan2] when called with the vector's [member y] and [member x] as parameters: [code]atan2(y, x)[/code].
 			</description>
 		</method>
@@ -43,6 +44,7 @@
 			<argument index="0" name="to" type="Vector2" />
 			<description>
 				Returns the angle to the given vector, in radians.
+				[url=https://raw.githubusercontent.com/godotengine/godot-docs/master/img/vector2_angle_to.png]Illustration of the returned angle.[/url]
 			</description>
 		</method>
 		<method name="angle_to_point">
@@ -50,6 +52,7 @@
 			<argument index="0" name="to" type="Vector2" />
 			<description>
 				Returns the angle between the line connecting the two points and the X axis, in radians.
+				[url=https://raw.githubusercontent.com/godotengine/godot-docs/master/img/vector2_angle_to_point.png]Illustration of the returned angle.[/url]
 			</description>
 		</method>
 		<method name="aspect">