fix even more broken markdown links

Added `bin/find-missing-links.sh` tool to check for
markdown links to missing local files.

Regarding the missing link tool:

```
    Here be extended regular expression magic dragons! :-)
```

Added `make find_missing_links` to the top level Makefile.

Added `make find_missing_links` to `make www` and `make quick_www`.

Ran `make www` to perform the above.

TODO: Fix markdown links to missing local files.

2012/endoh1/README.md

@@ -292,7 +292,7 @@ casting) it to an integer-type variable.
 [pour-out.txt](%%REPO_URL%%/2012/endoh1/pour-out.txt) pours you a cup of tea.
 
 [tanada.txt](%%REPO_URL%%/2012/endoh1/tanada.txt) simulates "Terrace farming".  ("Tanada" means a
-"[terraced rice](https://en.wikipedia.org/wiki/Terrace_(earthworks) fields)" in Japanese.)
+"[terraced rice](https://en.wikipedia.org/wiki/Terrace_(earthworks) fields)" in Japanese.)
 
 [clock.txt](%%REPO_URL%%/2012/endoh1/clock.txt) is a "water" clock created by HAMANO Tsukasa.