refactor configure script

Generate a makefile config instead of a makefile with predefined
constants. This makes the build a bit more easier to modify. Also
improve the makefile and apply some suggestions from shellcheck. :)

Makefile

@@ -0,0 +1,29 @@
+IMPORT    = import
+PREFIX    = /usr/local
+MANPREFIX = ${PREFIX}/man
+
+DC      = ${_DC}
+CFLAGS  = ${_CFLAGS}
+OBJS    = ${_OBJS}
+
+all: esv
+
+include config.mk
+
+esv: ${OBJS}
+	${DC} ${_LDFLAGS} -of=$@ ${OBJS}
+
+.SUFFIXES: .d .o
+
+.d.o:
+	${DC} ${CFLAGS} -c $<
+
+clean:
+	rm -f esv ${OBJS} ${INIOBJS}
+
+install: esv
+	install -Dm755 esv ${DESTDIR}${PREFIX}/bin/esv
+	install -Dm644 esv.1 ${DESTDIR}${MANPREFIX}/man1
+	install -Dm644 esv.conf.5 ${DESTDIR}${MANPREFIX}/man5
+
+.PHONY: all clean install