Gluing grapheme concepts

By de-indexing some of them, linking others, and generally reviewing
what #891 requires. This closes #891 as far as the original issue
title is concerned; however, I would say another issue should be open
to actually explain how to work with that kind of regexes (if it's not
done already)

Author: JJ

doc/Language/unicode.pod6

@@ -56,7 +56,7 @@ X<|UTF8-C8>
 X<UTF-8 Clean-8> is an encoder/decoder that primarily works as the UTF-8 one.
 However, upon encountering a byte sequence that will either not decode as
 valid UTF-8, or that would not round-trip due to normalization, it will use
-NFG synthetics to keep track of the original bytes involved. This means that
+L<NFG synthetics|/language/glossary#NFG> to keep track of the original bytes involved. This means that
 encoding back to UTF-8 Clean-8 will be able to recreate the bytes as they
 originally existed. The synthetics contain 4 codepoints:
 

doc/Type/Cool.pod6

@@ -707,10 +707,10 @@ number of characters in the string. Please note that on the JVM, you currently g
 codepoints instead of graphemes.
 
     say 'møp'.chars;    # OUTPUT: «3␤»
-    say 'ã̷̠̬̊'.chars;      # OUTPUT: «1␤»
-    say '👨‍👩‍👧‍👦🏿'.chars;      # OUTPUT: «1␤»
+    say 'ã̷̠̬̊'.chars;     # OUTPUT: «1␤»
+    say '👨‍👩‍👧‍👦🏿'.chars;    # OUTPUT: «1␤»
 
-X<|Grapheme> X<|NFG>
+X<|Grapheme>
 
 Graphemes are user visible characters. That is, this is what the user
 thinks of as a “character”.
@@ -730,7 +730,7 @@ order to see how it is going to behave:
 
 You can read more about graphemes in the
 L<Unicode Standard|http://unicode.org/reports/tr29/#Grapheme_Cluster_Boundaries>,
-which Perl 6 tightly follows.
+which Perl 6 tightly follows, using a method called L<NFG, normal form graphemes|/language/glossary#NFG> for efficiently representing them.
 
 =head2 routine codes