Add preview of 1984-2019

The 2020 winners are hinted it, but the source code is not there,
nor are the hints. Someone could look into the HTML and
see what was commented out, but that is not a problem because
WHO won is known and the name of their AWARD is known already.
Moreover a number of the winners have talked about what their
entirs do, so the commented out spoiler text is not a bit problem.

One will find HTML commented out with:

    <!-- XXX remove when 2020 is ready
    2020 links here
    XXX remove when 2020 is ready -->

The "XXX remove when 2020 is ready" string is found at the
start and end comment blocks.  Again, soneone could read
what was commented out, but that is OK since most of that
information is known or can be known.  The following files
have such HTML comment blocks in them.

    ./winners.html
    ./years-spoiler.html
    ./years.html

In addition, ./all/summary.txt was modified to not
include the 2020 entries for the momemt.

The 2020 winner code AND write-ups are NOT part of this set.

p.s. The all/all.tar.bz2 does not contain the 2020 source code (yet?).

2015/muth/machine_gcd.h

@@ -0,0 +1,56 @@
+/*
+ * greatest common divisor
+ *
+ * based on http://www.ioccc.org/2001/herrmann1.gcd
+ */
+
+// try tape_15_50.h or tape_77_55.h
+
+#define A__  (_, R, A )
+#define A_1  (1, L, x9)
+
+#define x0_1 (_, R, x1)
+
+#define x1__ (_, R, xa)
+#define x1_1 (1, R, x2)
+
+#define x2__ (_, R, x3)
+#define x2_1 (1, R, x2)
+
+#define x3__ (_, R, x3)
+#define x3_1 (1, R, x4)
+
+#define x4__ (1, L, x5)
+#define x4_1 (1, R, x4)
+
+#define x5_1 (_, L, x6)
+
+#define x6__ (_, R, xc)
+#define x6_1 (1, L, x7)
+
+#define x7__ (_, L, x8)
+#define x7_1 (1, L, x7)
+
+#define x8__ (_, L, x8)
+#define x8_1 (1, L, x9)
+
+#define x9__ (1, R, x0)
+#define x9_1 (1, L, x9)
+
+#define xa__ (_, R, xa)
+#define xa_1 (_, R, xb)
+
+#define xb__ (_, R, xf)
+#define xb_1 (1, R, xc)
+
+#define xc__ (_, R, xd)
+#define xc_1 (1, R, xc)
+
+#define xd__ (_, L, xe)
+#define xd_1 (_, R, xd)
+
+#define xe__ (_, L, xe)
+#define xe_1 (1, L, x7)
+
+#define xf__ (_, break)
+#define xf_1 (_, R, xf)