doc: Sync classref with current source

doc/classes/Color.xml

@@ -308,9 +308,6 @@
 		</member>
 	</members>
 	<constants>
-		<constant name="gray" value="Color( 0.75, 0.75, 0.75, 1 )">
-			Gray color.
-		</constant>
 		<constant name="aliceblue" value="Color( 0.94, 0.97, 1, 1 )">
 			Alice blue color.
 		</constant>
@@ -461,6 +458,9 @@
 		<constant name="goldenrod" value="Color( 0.85, 0.65, 0.13, 1 )">
 			Goldenrod color.
 		</constant>
+		<constant name="gray" value="Color( 0.75, 0.75, 0.75, 1 )">
+			Gray color.
+		</constant>
 		<constant name="green" value="Color( 0, 1, 0, 1 )">
 			Green color.
 		</constant>

doc/classes/Image.xml

@@ -430,6 +430,12 @@
 				Saves the image as a PNG file to [code]path[/code].
 			</description>
 		</method>
+		<method name="save_png_to_buffer" qualifiers="const">
+			<return type="PoolByteArray">
+			</return>
+			<description>
+			</description>
+		</method>
 		<method name="set_pixel">
 			<return type="void">
 			</return>

doc/classes/OS.xml

@@ -954,7 +954,7 @@
 		<member name="screen_orientation" type="int" setter="set_screen_orientation" getter="get_screen_orientation" enum="_OS.ScreenOrientation" default="0">
 			The current screen orientation.
 		</member>
-		<member name="tablet_driver" type="String" setter="set_current_tablet_driver" getter="get_current_tablet_driver" default="&quot;wintab&quot;">
+		<member name="tablet_driver" type="String" setter="set_current_tablet_driver" getter="get_current_tablet_driver" default="&quot;&quot;">
 			The current tablet drvier in use.
 		</member>
 		<member name="vsync_enabled" type="bool" setter="set_use_vsync" getter="is_vsync_enabled" default="true">

doc/classes/ProjectSettings.xml

@@ -460,7 +460,7 @@
 		<member name="display/window/size/width" type="int" setter="" getter="" default="1024">
 			Sets the game's main viewport width. On desktop platforms, this is the default window size. Stretch mode settings also use this as a reference when enabled.
 		</member>
-		<member name="display/window/tablet_driver" type="String" setter="" getter="" default="&quot;wintab&quot;">
+		<member name="display/window/tablet_driver" type="String" setter="" getter="" default="&quot;&quot;">
 			Specifies the tablet driver to use. If left empty, the default driver will be used.
 		</member>
 		<member name="display/window/vsync/use_vsync" type="bool" setter="" getter="" default="true">