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/AudioEffectEQ21.xml

@@ -5,28 +5,28 @@
 		Each frequency can be modulated between -60/+24 dB.
 	</brief_description>
 	<description>
-		Frequency bands :
-		Band 1 : 22 Hz
-		Band 2 : 32 Hz
-		Band 3 : 44 Hz
-		Band 4 : 63 Hz
-		Band 5 : 90 Hz
-		Band 6 : 125 Hz
-		Band 7 : 175 Hz
-		Band 8 : 250 Hz
-		Band 9 : 350 Hz
-		Band 10 : 500 Hz
-		Band 11 : 700 Hz
-		Band 12 : 1000 Hz
-		Band 13 : 1400 Hz
-		Band 14 : 2000 Hz
-		Band 15 : 2800 Hz
-		Band 16 : 4000 Hz
-		Band 17 : 5600 Hz
-		Band 18 : 8000 Hz
-		Band 19 : 11000 Hz
-		Band 20 : 16000 Hz
-		Band 21 : 22000 Hz
+		Frequency bands:
+		Band 1: 22 Hz
+		Band 2: 32 Hz
+		Band 3: 44 Hz
+		Band 4: 63 Hz
+		Band 5: 90 Hz
+		Band 6: 125 Hz
+		Band 7: 175 Hz
+		Band 8: 250 Hz
+		Band 9: 350 Hz
+		Band 10: 500 Hz
+		Band 11: 700 Hz
+		Band 12: 1000 Hz
+		Band 13: 1400 Hz
+		Band 14: 2000 Hz
+		Band 15: 2800 Hz
+		Band 16: 4000 Hz
+		Band 17: 5600 Hz
+		Band 18: 8000 Hz
+		Band 19: 11000 Hz
+		Band 20: 16000 Hz
+		Band 21: 22000 Hz
 		See also [AudioEffectEQ], [AudioEffectEQ6], [AudioEffectEQ10].
 	</description>
 	<tutorials>