Introduce 'libs'

Recursively search libs/* for source and include dirs

Move mgos_barometer code to its own subdir, in preparation for release
to GitHub.

Makefile

@@ -1,6 +1,6 @@
 TARGET  = mgos_i2c
 CC      = gcc
-CFLAGS  = -g -O -Wall -I include/
+CFLAGS  = -g -O -Wall
 LINKER  = gcc
 LFLAGS  = -O -Wall -I. -lm
 
@@ -12,21 +12,24 @@ all: default
 SRCDIR  = src
 INCDIR  = include
 OBJDIR  = build
+LIBDIR  = libs
 BINDIR  = .
 
-SOURCES  := $(wildcard $(SRCDIR)/*.c) 
-INCLUDES := $(wildcard $(SRCDIR)/*.h)
-OBJECTS  := $(SOURCES:$(SRCDIR)/%.c=$(OBJDIR)/%.o)
+SRCS     := $(shell find $(SRCDIR) $(LIBDIR) -type f -name '*.c')
+INCS     := $(shell find $(SRCDIR) $(LIBDIR) $(INCDIR) -type d -name 'include')
+INCFLAGS := $(patsubst %,-I %, $(INCS))
+OBJS     := $(patsubst %.c, build/%.o, $(SRCS))
 RM       = rm -f
+RMDIR    = rm -r -f
 
+$(BINDIR)/$(TARGET): $(OBJS)
+	$(LINKER) $(OBJS) $(LFLAGS) -o $@
 
-$(BINDIR)/$(TARGET): $(OBJECTS)
-	$(LINKER) $(OBJECTS) $(LFLAGS) -o $@
-
-$(OBJECTS): $(OBJDIR)/%.o : $(SRCDIR)/%.c
-	$(CC) $(CFLAGS) -c $< -o $@
+$(OBJS): $(OBJDIR)/%.o : %.c
+	@mkdir -p $(shell dirname $(OBJS))
+	$(CC) $(CFLAGS) $(INCFLAGS) -c $< -o $@
 
 .PHONY: clean
 clean:
-	$(RM) $(OBJECTS)
+	$(RMDIR) $(OBJDIR)
 	$(RM) $(BINDIR)/$(TARGET)