fix more broken markdown links

We fix more markdown links in markdown files that refer to files
internally to the web site.

Added tmp tools to find and print various markdown links:

* `tmp/md-links.sh` - print all markdown links
* `tmp/md-token-links.sh` - print all markdown links that start with a **%%TOKEN%%**
* `tmp/md-local-links.sh` - print all markdown links to a local file
* `tmp/md-link-paths.sh` - print local file paths referenced in markdown links

Fixed a number of markdown formatting problems with `thanks-for-help.md`.
Fixed markdown links to files in `thanks-for-help.md`.  Improved
heading levels in `thanks-for-help.md`, and made entry sections consistent.

Changed all markdown links that end in "))" to end in a better way.

Explained in `markdown.md` why we are avoiding markdown links that
end in "))".

Ran `make www` to perform the above.

TODO: Fix stuff we broke by mistake doing the above.

TODO: Fix more broken markdown links.

1998/schnitzi/README.md

@@ -77,8 +77,8 @@ the letter `e`.
 
 The IOCCC has been no stranger to this concept.  Several winning entries from
 years past have accomplished interesting feats while completely avoiding the use
-of certain C constructs thought to be essential (e.g.
-[1988/robison.c](%%REPO_URL%%/1988/robison/robison.c)).  If you have to ask why they would
+of certain C constructs thought to be essential (e.g.,
+[1988/robison.c](%%REPO_URL%%/1988/robison/robison.c) file).  If you have to ask why they would
 do it this way, then this contest just isn't for you.
 
 In continuing with this fine tradition, this program suggests to the ANSI

1998/schnitzi/index.html

@@ -441,8 +441,8 @@ entire novel (E. V. Wright’s “Gadsby”) in which no word contains
 the letter <code>e</code>.</p>
 <p>The IOCCC has been no stranger to this concept. Several winning entries from
 years past have accomplished interesting feats while completely avoiding the use
-of certain C constructs thought to be essential (e.g.
-<a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1988/robison/robison.c">1988/robison.c</a>). If you have to ask why they would
+of certain C constructs thought to be essential (e.g.,
+<a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1988/robison/robison.c">1988/robison.c</a> file). If you have to ask why they would
 do it this way, then this contest just isn’t for you.</p>
 <p>In continuing with this fine tradition, this program suggests to the ANSI
 committee some new practical simplifications for the C language. For instance,