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.

2013/hou/README.md

@@ -39,11 +39,17 @@ you leave the program running overnight to see what happens. If however you do
 not have all night :-) then the following JPEG files should show you what
 happens with some of the invocations above:
 
-![./hou BIG - Luna](luna.jpg)
+<img src="luna.jpg"
+ alt="artificial image showing a room lit by light from a window"
+ width=640 height=480>
 
-![./hou old_default.scene - Old default](old_default.jpg)
+<img src="old_default.jpg"
+ alt="artificial image showing IOCCC 2013 in a room with stars on the floor and double helix in the backgrond"
+ width=640 height=480>
 
-![./hou otherroom.scene - Other room](otherroom.jpg)
+<img src="otherroom.jpg"
+ alt="artificial image the background double helix"
+ width=320 height=240>
 
 This program does not terminate by itself: you must kill `hou` (but not Qiming
 Hou :-) ) in order to end the program.