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/Curve3D.xml

@@ -1,11 +1,11 @@
 <?xml version="1.0" encoding="UTF-8" ?>
 <class name="Curve3D" inherits="Resource" category="Core" version="3.2">
 	<brief_description>
-		Describes a Bezier curve in 3D space.
+		Describes a Bézier curve in 3D space.
 	</brief_description>
 	<description>
-		This class describes a Bezier curve in 3D space. It is mainly used to give a shape to a [Path], but can be manually sampled for other purposes.
-		It keeps a cache of precalculated points along the curve, to speed further calculations up.
+		This class describes a Bézier curve in 3D space. It is mainly used to give a shape to a [Path], but can be manually sampled for other purposes.
+		It keeps a cache of precalculated points along the curve, to speed up further calculations.
 	</description>
 	<tutorials>
 	</tutorials>
@@ -22,7 +22,7 @@
 			<argument index="3" name="at_position" type="int" default="-1">
 			</argument>
 			<description>
-				Adds a point to a curve, at [code]position[/code], with control points [code]in[/code] and [code]out[/code].
+				Adds a point to a curve at [code]position[/code], with control points [code]in[/code] and [code]out[/code].
 				If [code]at_position[/code] is given, the point is inserted before the point number [code]at_position[/code], moving that point (and every point after) after the inserted point. If [code]at_position[/code] is not given, or is an illegal value ([code]at_position &lt;0[/code] or [code]at_position &gt;= [method get_point_count][/code]), the point will be appended at the end of the point list.
 			</description>
 		</method>