DEV: flags: replace the unneeded makefile with a README

The makefile was not suited anymore as it didn't consider all
required compiler options and was causing way too many build
warnings with modern compilers. Let's just remove it and indicate
that this has to be built from the top of the project.

dev/flags/Makefile

@@ -1,14 +0,0 @@
-INCLUDE  = -I../../include
-
-CC       = gcc
-OPTIMIZE = -O2
-DEFINE   =
-OBJS     = flags
-
-all: $(OBJS)
-
-flags: flags.c
-	$(CC) $(OPTIMIZE) $(DEFINE) $(INCLUDE) -o $@ $^
-
-clean:
-	rm -f $(OBJS) *.[oas] *~

dev/flags/README

@@ -0,0 +1,12 @@
+This needs to be built from the top makefile, for example :
+
+    make dev/flags/flags
+
+Then the executable is usable either one value at a time from the
+command line, either with values coming from stdin with "-" passed
+alone instead of the value.
+
+It is possible to restrict the decoding to certain fields only by
+specifying one of "ana", "chn", "conn", "cs", "si", "sierr", "strm",
+"task", or "txn" before the value.
+