fix HTML problems associated with leading ---'s

Please do not use "**---**" in markdown lines to separate sections.

This causes `pandoc(1)` to generate "**\<hr />**".

The "**\<hr />**" has no effect in standard HTML 5 and interacts
badly with unquoted attribute values.

If a horizontal line is really needed, use "**\<hr>**".

If a short line is needed, use: "**\<hr
style="width:10%;text-align:left;margin-left:0">**"

1998/dorssel/dorssel.html

@@ -264,7 +264,7 @@ mind ;-)</p>
     l[12] - l[14]   strspn argument
     l[34]           terminator for backward decoding
     l[35] - l[998]  input line</code></pre>
-<hr />
+<hr style="width:10%;text-align:left;margin-left:0">
 <p>Selected notes:
 - We don’t need to declare <code>isalnum(3)</code> (or include ctype.h) as its implicit
 declaration is correct (int argument, int result). This is not so for
@@ -276,7 +276,7 @@ whereas it is not. Well, it is, but there is a sequence point in between.
 - lclint 2.4b parses line 13 as <error>, whereas it is correct code.
 - lclint 2.4b is positive the second <code>while</code> loop is infinite, whereas it is
 not.</p>
-<hr />
+<hr style="width:10%;text-align:left;margin-left:0">
 <p>.. - …. .. -. -.- - …. .. … … .–. — .. .-.. . .-. .. … – — .-. . — -… ..-. ..- … -.-. .- - . -.. - …. .- -. - …. . .–. .-. — –. .-. .- –</p>
 <p>. -..- . .-. -.-. .. … .
 -.-. …. .- -. –. . - …. . .–. .-. — –. .-. .- – … — .. - -.. — . … -. — - … …. — ..- -</p>