Adds a section on :pack

Although it was rather well covered in the Blob page. Added some
references, and changed definitions on that page.

Author: JJ

doc/Language/experimental.pod6

@@ -20,7 +20,36 @@ later.)
 =comment The following should be a table but formatting in tables is
 not yet rendered properly.
 
-=item X<B<pack>|pack> [TBD]
+=head2 X<B<pack>|pack>
+
+Pack is a feature that allows binary serialization of general data structures,
+and is inherited from
+L<Perl's pack|http://perldoc.perl.org/functions/pack.html>.
+The C<pack> order creates a
+C<Buf> by packing data structures in a certain way given by a I<packing string>
+with the options shown
+L<in the description of C<unpack>\/type/Blob#method_unpack>.
+
+For instance, we can pack numbers interpreting them as hexadecimal (C<H>) with
+the pattern repeating until there are no more elements (C<*>):
+
+=for code
+use experimental :pack;
+say pack("H*", "414243").contents;#  OUTPUT: «(65 66 67)␤»
+
+There is a corresponding C<unpack> routine that does exactly the opposite.
+
+=for code
+use experimental :pack;
+my $buf=Buf.new(65,66,67);
+say $buf.unpack("H*"); # OUTPUT: «414243␤»
+
+
+Not all of the symbols above are guaranteed to be implemented, and the roadmap
+does not include a fixed date for getting out of that stage.
+
+Please see also documentation for L<C<pack>\/type/Blob#sub_pack> and
+L<C<unpack>\/type/Blob#method_unpack> in the C<Blob> page.
 
 =head2 X<B<macros>|macros>
 

doc/Type/Blob.pod6

@@ -137,14 +137,17 @@ values are given to fill the entire C<Blob>.
 
 =head2 method unpack
 
-This method is considered B<experimental>, in order to use it you will need to do:
+This method is considered B<experimental>, in order to use it you will need to
+do:
 
     use experimental :pack;
 
-
 Defined as:
 
-    method unpack(Blob:D: $template --> List:D)
+    method unpack(Blob:D: Str:D $template)
+    method unpack(Blob:D: @template)
+    multi sub unpack(Blob:D \blob, Str:D $template)
+    multi sub unpack(Blob:D \blob, @template)
 
 Extracts features from the blob according to the template string, and
 returns them as a list.
@@ -187,13 +190,15 @@ Example:
 
 =head2 sub pack
 
-This subroutine is considered B<experimental>,  in order to use it you will need to do:
+This subroutine is considered B<experimental>,  in order to use it you will need
+to do:
 
 =for code
 use experimental :pack;
 
 =for code
-sub pack(Str $template, *@items --> Buf)
+sub pack(Str $template, *@items)
+sub pack(@template, *@items)
 
 Packs the given items according to the template and returns a buffer
 containing the packed bytes.