docs: Indent <since> tags.

Also updates the 'since' of applications/functions that existed before
XML documentation was introduced (1.6.2.0).

(cherry picked from commit 174006fcaa)

main/pbx.c

@@ -96,7 +96,9 @@
 
 /*** DOCUMENTATION
 	<function name="EXCEPTION" language="en_US">
-		<since><version>1.6.2.0</version></since>
+		<since>
+			<version>1.6.0</version>
+		</since>
 		<synopsis>
 			Retrieve the details of the current dialplan exception.
 		</synopsis>
@@ -128,7 +130,9 @@
 		</see-also>
 	</function>
 	<function name="TESTTIME" language="en_US">
-		<since><version>1.8.0</version></since>
+		<since>
+			<version>1.8.0</version>
+		</since>
 		<synopsis>
 			Sets a time to be used with the channel to test logical conditions.
 		</synopsis>
@@ -201,7 +205,9 @@
 			</list-elements>
 			<managerEvent name="ExtensionStateListComplete" language="en_US">
 				<managerEventInstance class="EVENT_FLAG_COMMAND">
-					<since><version>13.0.0</version></since>
+					<since>
+						<version>13.0.0</version>
+					</since>
 					<synopsis>
 						Indicates the end of the list the current known extension states.
 					</synopsis>