some docs for arithmetic functions

manual/docs/en/dql-doctrine-query-language/functional-expressions.txt

@@ -55,5 +55,19 @@ foreach($users as $user) {
 
 
 +++ Arithmetic functions
+
+Availible DQL arithmetic functions:
+
+<code>
+ABS(simple_arithmetic_expression)
+SQRT(simple_arithmetic_expression)
+MOD(simple_arithmetic_expression, simple_arithmetic_expression)
+</code>
+
+* The //ABS// function returns the absolute value for given number. 
+
+* The //SQRT// function returns the square root for given number. 
+
+* The //MOD// function returns the modulus of first argument using the second argument.
+
 +++ Datetime functions
-+++ Collection functions