Add link to exceptions

Author: pablogsal

Doc/library/re.rst

@@ -29,9 +29,9 @@ a literal backslash, one might have to write ``'\\\\'`` as the pattern
 string, because the regular expression must be ``\\``, and each
 backslash must be expressed as ``\\`` inside a regular Python string
 literal. Also, please note that any invalid escape sequences in Python's
-usage of the backslash in string literals now generate a DeprecationWarning
-and in the future this will become a SyntaxError. This behaviour will happen
-even if it is a valid escape sequence for a regular expression.
+usage of the backslash in string literals now generate a :exc:`DeprecationWarning`
+and in the future this will become a :exc:`SyntaxError`. This behaviour
+will happen even if it is a valid escape sequence for a regular expression.
 
 The solution is to use Python's raw string notation for regular expression
 patterns; backslashes are not handled in any special way in a string literal