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/Physics2DDirectBodyState.xml

@@ -56,7 +56,7 @@
 			<argument index="1" name="impulse" type="Vector2">
 			</argument>
 			<description>
-				Applies a positioned impulse to the body. An impulse is time independent! Applying an impulse every frame would result in a framerate dependent force. For this reason it should only be used when simulating one-time impacts (use the "_force" functions otherwise). The offset uses the rotation of the global coordinate system, but is centered at the object's origin.
+				Applies a positioned impulse to the body. An impulse is time-independent! Applying an impulse every frame would result in a framerate-dependent force. For this reason, it should only be used when simulating one-time impacts (use the "_force" functions otherwise). The offset uses the rotation of the global coordinate system, but is centered at the object's origin.
 			</description>
 		</method>
 		<method name="apply_torque_impulse">
@@ -135,7 +135,8 @@
 			<return type="int">
 			</return>
 			<description>
-				Returns the number of contacts this body has with other bodies. Note that by default this returns 0 unless bodies are configured to log contacts. See [member RigidBody2D.contact_monitor].
+				Returns the number of contacts this body has with other bodies.
+				[b]Note:[/b] By default, this returns 0 unless bodies are configured to monitor contacts. See [member RigidBody2D.contact_monitor].
 			</description>
 		</method>
 		<method name="get_contact_local_normal" qualifiers="const">