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.

2013/hou/README.md

@@ -63,7 +63,7 @@ really just a decompressor to generate the real source code of the
 program.
 
 This program will loop infinitely while progressively refining a
-[raytraced](https://en.wikipedia.org/wiki/Ray_tracing_(graphics)) image.
+[raytraced](https://en.wikipedia.org/wiki/Ray_tracing_(graphics)) image.
 
 NOTE: the author refers to [a.c](%%REPO_URL%%/2013/hou/a.c), placed in a gzipped file `a.c.gz`. We do not
 include it but it can be generated like:
@@ -215,8 +215,9 @@ probability proportional to its energy, the sample distribution directly
 corresponds to the final image, which can then be produced as a simple per-pixel
 histogram of all generated paths. The robustness comes from a state mutation
 strategy that actively tries to explore the neighborhood of high energy peaks
-(e.g. paths that happen to hit the light source in
-[otherroom.scene](%%REPO_URL%%/2013/hou/otherroom.scene)). In addition, a rudimentary form of lens
+(e.g., paths that happen to hit the light source in
+[otherroom.scene](%%REPO_URL%%/2013/hou/otherroom.scene) file).
+In addition, a rudimentary form of lens
 path stratification is added to balance the attention each pixel receives. The
 Metropolis-Hasting process completely avoids the tell-tale pixel sampling loop
 required in most other image generation methods.
@@ -239,7 +240,8 @@ Metropolis-Hasting used an even worse PRNG in their 1953 paper.
 The `PPM` compressor uses statically weighted fixed order contexts with an
 arithmetic encoder tweaked for [iocccsize.c](%%REPO_URL%%/2013/iocccsize.c). The encoder emits octet-space pairs
 where each octet encodes ~6.5 bits of information and each space encodes 2 bits
-(thanks to the generous definition of "space" in [iocccsize.c](%%REPO_URL%%/2013/iocccsize.c)). The compressor
+(thanks to the generous definition of "space" in [iocccsize.c](%%REPO_URL%%/2013/iocccsize.c) code).
+The compressor
 actively shuffles the variable names around until the compressed string happens
 to contain enough `{}; `s to pass the final [iocccsize.c](%%REPO_URL%%/2013/iocccsize.c) test.
 There are a few other tweaks: