Fix assumption that EOF==-1 in 2015/schweikhardt

The author stated EOF must be -1 but this is, as the author even noted,
not guaranteed by the standard (it just has to be a value < 0).

But rather than add C pre-processor directives to force EOF to be -1
(preferred over changing EOF to -1 in the code) the Makefile does (after
${CFLAGS}) -UEOF -DEOF=-1 so as to not have to modify the code any.

A few fixes in the README.md file.

This should complete this entry, leaving just (I think) 2015/endoh1.

2015/schweikhardt/Makefile

@@ -129,7 +129,7 @@ all: data ${TARGET}
 	sandwich supernova deep_magic magic charon pluto
 
 ${PROG}: ${PROG}.c
-	${CC} ${CFLAGS} $< -o $@ ${LDFLAGS}
+	${CC} ${CFLAGS} -UEOF -DEOF=-1 $< -o $@ ${LDFLAGS}
 
 # alternative executable
 #

2015/schweikhardt/README.md

@@ -24,6 +24,9 @@ For more detailed information see [2015 schweikhardt in bugs.md](/bugs.md#2015-s
 
 where n is a base 16 number of any size.
 
+NOTE: although it's supposed to be a base 16 number nothing will stop you from
+doing something else. The author explains this in more details.
+
 
 ### Try:
 
@@ -31,6 +34,10 @@ where n is a base 16 number of any size.
 ./try.sh
 ```
 
+After running it once to see what commands are run, you might wish to run it a
+second time and just hold down space to see a fun scroll of numbers especially
+where zeroes move to the right.
+
 
 ## Judges' remarks:
 
@@ -445,7 +452,7 @@ In a certain way, the program is character set and encoding agnostic.
 
 * The `EOF` macro from `<stdio.h>` must expand to `-1` since it is used
 to decrement a pointer and do some other math.
-None of the tools catches this one. The program self-protects against unusual
+None of the tools catch this one. The program self-protects against unusual
 systems with `#if EOF + __STDC__` followed by `#error goofy!`. In the rare event
 your system is goofy, replace all `EOF` tokens with `(-1)` and remove the
 `#error` directive.