add hack-a-round for language specified markdown code blocks

When language is specified in a markdown code block such as:

````
```c
    printf("Hello, world!\n");
```
````

is used, the resulting HTML as produced by `pandoc(1)` combined
with our revised `ioccc.css` is not intent the code block well.

A temporary "_hack-a-round_" is to turn the "markdown code language
specifier" into an HTML comment.  For example:

````
```<!---c-->
    printf("Hello, world!\n");
```
````

This commits turns off existing markdown code language specifiers
for now, while preserving our ability to restore them in the future
when a better  "_hack-a-round_" to the "markdown code language
specifier" problem is found.

The HTML impact if this "_hack-a-round_" is to produce HTML that
looks like this:

```
<pre class="&lt;!---c--&gt;"><code> .. </code></pre>
```

We might be able to create a complex set of classes for each markdown
code language (there won't be very many) in `ioccc.css`, or we might
find a more general CSS (or maybe `pandoc(1)`?) solution.

For now, this hack-a-round will have to do.

2006/toledo2/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make
 ```
 
@@ -22,7 +22,7 @@ For more detailed information see [2006 toledo2 bugs](../../bugs.html#2006_toled
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./toledo2
 ```
 
@@ -33,7 +33,7 @@ does not seem to happen in macOS or linux in 2023.
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./toledo2
 ```
 
@@ -56,7 +56,7 @@ functions in place of `read(2)` and `write(2)`.
 
 ### Alternate build:
 
-```sh
+```<!---sh-->
     make alt
 ```
 
@@ -112,7 +112,7 @@ Journal](https://en.wikipedia.org/wiki/Dr._Dobb%27s_Journal).
 Type using uppercase letters. Here are three example programs. Press Enter after
 each line:
 
-```basic
+```<!---basic-->
     10 PRINT "Hello, world!"
     LIST
     RUN
@@ -155,7 +155,7 @@ from the `SOURCE` directory:
 To import them, you must run the emulator with an argument, by
 example:
 
-```sh
+```<!---sh-->
     ./toledo2 DDT.COM
 ```