Change alt/orig to build/to use heading levels

As the 'Alternate code' and 'Original code' heading level is now 2 the
'To build' and 'To use' subsections should be level 3, not 4, and also
reworded, this was done:

    sgit -e 's/^#### To build/### Alternate build/g' -e 's/^#### To use/### Alternate use/g' '*README.md'

Many more have to be updated and this will be done manually at another
time.

1989/jar.1/README.md

@@ -30,7 +30,7 @@ make clobber all
 
 This code, which prints something slightly different, is provided as well.
 
-#### To build:
+### Alternate build:
 
 NOTE: this will run the program itself.
 
@@ -38,7 +38,7 @@ NOTE: this will run the program itself.
 make clobber alt
 ```
 
-#### To use:
+### Alternate use:
 
 Alternatively, you can run it directly: