fix HTML problems related to pandoc and markdown image notation

Improve `make clobber` for `2004/anonymous`.

Instead of using this markdown element to embed an image:

```
![alt text](filename.png "Title")
```

Use a "img" HTML element with "alt", "alt", "width" and "length"
attributes:

```
<img src="filename.png"
 alt="describe the filename.png image for someone who cannot view it"
 width=PIXEL_WIDTH height=PIXEL_HEIGHT>
```

This was performed for:

```
2004/anonymous/index.html
2005/boutines/index.html
2011/goren/index.html
2012/vik/index.html
2013/birken/index.html
2013/cable1/index.html
2013/cable3/index.html
2013/hou/doc/example.html
2013/hou/index.html
2020/ferguson1/chocolate-cake.html
```

In the case of `2013/cable1/index.html` we reduce the displayed
image size by a factor for 2.  There is **NO** need to downsize the image
as this image size reduction produces a clean and sharp looking image.

In the case of `2013/hou/index.html` we reduce the displayed
image size by a factor for 2.  There is **NO** need to downsize the image
as this image size reduction produces a clean and sharp looking image.

In the case of `2020/ferguson1/chocolate-cake.html` we reduce the displayed
image size by a factor for 4.  There is **NO** need to downsize the image
as this image size reduction produces a clean and sharp looking image.

Run `make www` to perform the above.

2004/anonymous/Makefile

@@ -203,6 +203,7 @@ clean:
 
 clobber: clean
 	${RM} -f ${TARGET} ${ALT_TARGET}
+	${RM} -f precious.pgm ring.pgm
 	${RM} -rf *.dSYM
 	@-if [ -e sandwich ]; then \
 	    ${RM} -f sandwich; \

2004/anonymous/index.html

@@ -198,7 +198,7 @@ it. The real text is:</p>
 Speech</a>:</p>
 <p><img src="One_Ring_inscription.png"
  alt="The inscription, in the Black Speech of Mordor, on the One Ring"
- width=453 height=127></p>
+ width=690 height=127></p>
 <p>into English reads:</p>
 <pre><code>    One Ring to rule them all,
     One Ring to find them,