Proofread and improve the whole class reference

- Document a few more properties and methods
- Add more information to many classes
- Fix lots of typos and gramar mistakes
- Use [code] tags for parameters consistently
- Use [b] and [i] tags consistently
- Put "Warning:" and "Note:" on their own line to be more visible,
  and make them always bold
- Tweak formatting in code examples to be more readable
- Use double quotes consistently
- Add more links to third-party technologies

modules/opensimplex/doc_classes/OpenSimplexNoise.xml

@@ -42,7 +42,7 @@
 			</argument>
 			<description>
 				Returns the 1D noise value [code][-1,1][/code] at the given x-coordinate.
-				Note: This method actually returns the 2D noise value [code][-1,1][/code] with fixed y-coordinate value 0.0.
+				[b]Note:[/b] This method actually returns the 2D noise value [code][-1,1][/code] with fixed y-coordinate value 0.0.
 			</description>
 		</method>
 		<method name="get_noise_2d">
@@ -108,7 +108,7 @@
 			<argument index="0" name="size" type="int">
 			</argument>
 			<description>
-				Generate a tileable noise image, based on the current noise parameters. Generated seamless images are always square ([code]size[/code] x [code]size[/code]).
+				Generate a tileable noise image, based on the current noise parameters. Generated seamless images are always square ([code]size[/code] × [code]size[/code]).
 			</description>
 		</method>
 	</methods>