Mass fixes to headers in README.md files

There were many many README.md files with the wrong heading level for
different sections. These have been changed.

To help go through the changes it should be noted I used sgit and also
here is what is changed:

The 'Try', 'To build' and 'To run' lines have two '#'s. Some had one and
others had three.

An exception is that in 1984/anonymous/README.md for the alternative
code that had three '#'s. This is not consistent yet and it might be
that only two are desired. But for now that one at least has three.

2000/bmeyer/README.md

@@ -7,19 +7,19 @@
     Australia
     http://byron.csse.monash.edu.au/
     
-# To build:
+## To build:
 
 ```sh
 make
 ```
 
-### To run:
+## To run:
 
 ```sh
 ./bmeyer
 ```
 
-### Try:
+## Try:
 
 In a video window (white text on black background):