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

doc/classes/AnimationNodeBlendSpace1D.xml

@@ -22,7 +22,7 @@
 			<argument index="2" name="at_index" type="int" default="-1">
 			</argument>
 			<description>
-				Add a new point that represents a [code]node[/code] on the virtual axis at a given position set by [code]pos[/code]. You can insert it at a specific index using the [code]at_index[/code] argument. If you use the default value for [code]at_index[/code] , the point is inserted at the end of the blend points array.
+				Adds a new point that represents a [code]node[/code] on the virtual axis at a given position set by [code]pos[/code]. You can insert it at a specific index using the [code]at_index[/code] argument. If you use the default value for [code]at_index[/code] , the point is inserted at the end of the blend points array.
 			</description>
 		</method>
 		<method name="get_blend_point_count" qualifiers="const">