Minor updates to several README.md files

Just some formatting fixes and in some cases add links to XQuartz for
macOS Mountain Lion and beyond. More entries (probably many more) have
to have that link added but those will be found and fixed in time.

2018/anderson/README.md

@@ -1,20 +1,20 @@
 # Most able to divine code gaps
 
     Derek Anderson  
-`
-# To build:
+
+## To build:
 
 ```sh
 make
 ```
 
-### To run:
+## To run:
 
 ```sh
 ./prog < textfile
 ```
 
-### Try:
+## Try:
 
 ```sh
 ./prog < prog.c
@@ -22,7 +22,7 @@ make
 ./prog < README.md
 ```
 
-### Alternate code:
+## Alternate code:
 
 An alternate version of this entry, `prog.alt.c`, is provided.
 
@@ -45,7 +45,7 @@ With this entry, you won't need to turn your monitor [upside down](http://en.wik
 
 ## Author's comments:
 
-### Compiling the program
+### Compiling the program:
 
 ```sh
 cc -Wall -Wextra -Wpedantic -O3 -std=c11 prog.c -o prog

2018/poikola/README.md

@@ -3,19 +3,25 @@
     Timo Poikola <ioccc2018@ig.fi>  
     <https://ig.fi/>  
 
-# To build:
+## To build:
 
 ```sh
 make
 ```
 
-### To run:
+NOTE: this entry requires `X11/Xlib.h` header file and the X11 library to
+compile. macOS users running Mountain Lion and later will need to download and
+install [XQuartz](https://www.xquartz.org) in order to compile and run this
+entry.
+
+
+## To run:
 
 ```sh
 ./prog
 ```
 
-### Try:
+## Try:
 
 On terminal supports 24 bit color, has black background, and size at least 125x38, try:
 
@@ -72,7 +78,7 @@ This entry has partial support for terminals with a white background but the bes
 has a black background and the size is at least 125x38.
 
 Special note for Mac users: __Terminal__ does not work as expected you might need xterm from XQuartz or some other
-working terminal. Thanks to Dave Burton for spotting this problem.
+working terminal. Thanks to [Dave Burton](/winners.html#Dave_Burton) for spotting this problem.
 
 The main reason for the header `unistd.h` is `getdelim()` but once I included it I also abused other functions and defines. This header is mutually exclusive with _-std=c11_.
 
@@ -116,11 +122,12 @@ If you think you understand how this program works, can you answer these questio
 4. How do you change a single bit, without changing the functionality?
 
 
-### Rot18ed part
+### Rot18 part
 
 Because the rot13 is too easy to decode with the plain eyes, I decided to use the Caesar cipher with the key 18.
 
-Lzw xajkl tsffwj ak wfugvwv mkafy AWWW 754 xdgslk gf dafw 47. Al ak hjaflwv gfdq gf dalldw-wfvasf esuzafwk.
+    Lzw xajkl tsffwj ak wfugvwv mkafy AWWW 754 xdgslk gf dafw 47. Al ak hjaflwv
+    gfdq gf dalldw-wfvasf esuzafwk.
 
 ## Copyright and CC BY-SA 4.0 License: