Fix invalid use of markdown syntax in classref

Also:
* changed `[b]true[/b]` to `[code]true[/code]`
* use `[i]` for mathematical constant "e"
* use `[b]` for button text & menu item text
* improve markups about "tap1" and "tap2" in AudioEffectDelay

doc/classes/NavigationMeshSourceGeometryData3D.xml

@@ -54,7 +54,7 @@
 		<method name="has_data">
 			<return type="bool" />
 			<description>
-				Returns [b]true[/b] when parsed source geometry data exists.
+				Returns [code]true[/code] when parsed source geometry data exists.
 			</description>
 		</method>
 		<method name="set_indices">