(file-handler)+impl file for file handling

In particular I've implemented a standardised complete FILE * reader
without relying on fseek (which may not work for pipes).

Makefile

@@ -1,7 +1,7 @@
 CC=gcc
 CFLAGS=-Wall -Wextra -pedantic -ggdb -fsanitize=address
 LIBS=-lm -lraylib
-OBJECTS=main.o
+OBJECTS=file-handler.o main.o
 OUT=sandpile.out
 ARGS=