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.

2018/endoh2/README.md

@@ -38,7 +38,7 @@ sketch [comté](https://en.wikipedia.org/wiki/Comté_cheese) called ["Dead
 Parrot"](https://en.wikipedia.org/wiki/Dead_Parrot_sketch) from the British
 sitcom ["Monty Python's Flying Circus"](https://en.wikipedia.org/wiki/Monty_Python%27s_Flying_Circus)
 The "_Python_" in the award name refers to Monty Python, **not** the
-[programming language Python](https://en.wikipedia.org/wiki/Python_(programming_language)
+[programming language Python](https://en.wikipedia.org/wiki/Python_(programming_language)
 (the name of the programming language Python is derived from Monty Python).
 
 The shape of [prog.c](%%REPO_URL%%/2018/endoh2/prog.c) is "Undead Parrot" based on "dead parrot". The