💡 Add source documentation from recent conversations.

There have been some conversations in the last weeks which explained
several parts of the code, so add it to the source code documentation.
Also some other small source code documentation improvements.

boot.php

@@ -2009,7 +2009,7 @@ function build_querystring($params, $name = null) {
 }
 
 
-/*
+/**
  * @brief Much better way of dealing with c-style args.
  */
 function argc() {
@@ -2030,6 +2030,8 @@ function dba_timer() {
 /**
  * @brief Returns xchan_hash from the observer.
  *
+ * Observer can be a local or remote channel.
+ *
  * @return string xchan_hash from observer, otherwise empty string if no observer
  */
 function get_observer_hash() {
@@ -2040,7 +2042,6 @@ function get_observer_hash() {
 	return '';
 }
 
-
 /**
  * @brief Returns the complete URL of the current page, e.g.: http(s)://something.com/network
  *