sch2fig/main.c (read_file): move to file.c

This is to allow further I/O abstraction, later.

sch2fig/Makefile

@@ -12,6 +12,7 @@
 
 NAME = sch2fig
 OBJS = main.o sch-parse.o sch-render.o lib-parse.o lib-render.o \
+       file.o \
        style.o fig.o cairo.o gfx.o dwg.o text.o misc.o
 
 CFLAGS = -g -O -Wall -Wextra -Wno-unused-parameter -Wshadow \