Improving presence of escape characters in the documentation

Suggestion for a new section has not been considered, since escape
characters are standard and they behave in the standard way. However,
some indexing and a list of all escape characters has been added. This
closes #2313.

Author: JJ

doc/Language/quoting.pod6

@@ -90,6 +90,7 @@ Short       Long            Meaning
 :v          :val            Convert to allomorph if possible
 =end table
 
+X<|escaping quote>
 =head2 X<Escaping: q|quote,q;quote,' '>
 
 =begin code :skip-test

doc/Language/regexes.pod6

@@ -354,6 +354,7 @@ You can include Unicode properties in the list as well:
     /<:Zs + [\x9] - [\xA0]>/
     # Any character with "Zs" property, or a tab, but not a newline
 
+X<|escaping characters>
 You can use C<\> to escape characters that would have some meaning in the
 regular expression:
 

doc/Language/syntax.pod6

@@ -155,8 +155,8 @@ say "world";
 
 =head2 Comments
 
-Comments are parts of the program text which are only intended for human readers;
-the Perl 6 compilers do not evaluate them as program text.
+Comments are parts of the program text which are only intended for human
+readers; the Perl 6 compilers do not evaluate them as program text.
 
 Comments count as whitespace in places where the absence or presence of
 whitespace disambiguates possible parses.
@@ -454,7 +454,8 @@ String literals are surrounded by quotes:
     say 'a string literal';
     say "a string literal\nthat interprets escape sequences";
 
-See L<quoting|/language/quoting> for many more options.
+See L<quoting|/language/quoting> for many more options. Perl 6 uses the standard
+escape characters in literals: C<\' \" \\ \n \r \t \b \f \v \0>.
 
 =head3 X<Number literals|0b (radix form);0d (radix form);0o (radix form);0x (radix form)>