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