Add a skeleton for the library

There are now a few extra lines in the Makefile that make the PD Buddy
firmware library's makefile get included, and the variables it defines
get used.  There's no code to compile or include yet though.

Makefile

 
 # Imported source files and paths
 CHIBIOS = ChibiOS
+PDBLIB = lib
 # Startup files.
 include $(CHIBIOS)/os/common/ports/ARMCMx/compilers/GCC/mk/startup_stm32f0xx.mk
 # HAL-OSAL files (optional).
 include $(CHIBIOS)/os/rt/ports/ARMCMx/compilers/GCC/mk/port_v6m.mk
 # Other files (optional).
 include $(CHIBIOS)/test/rt/test.mk
+include $(PDBLIB)/pd-buddy.mk
 
 # Define linker script file here
 LDSCRIPT=$(CHIBIOS)/../ld/STM32F072x8.ld
        $(BOARDSRC) \
        $(TESTSRC) \
        $(CHIBIOS)/os/hal/lib/streams/chprintf.c \
+       $(PDBSRC) \
        $(wildcard src/*.c)
 
 # C++ sources that can be compiled in ARM or THUMB mode depending on the global
 INCDIR = $(STARTUPINC) $(KERNINC) $(PORTINC) $(OSALINC) \
          $(HALINC) $(PLATFORMINC) $(BOARDINC) $(TESTINC) \
          $(CHIBIOS)/os/hal/lib/streams $(CHIBIOS)/os/various \
+	 $(PDBINC) \
 	 config
 
 #

lib/pd-buddy.mk

+# Source files for the PD Buddy firmware library
+PDBSRC = $(wildcard $(PDBLIB)/src/*.c)
+
+# Include directories
+PDBINC = $(PDBLIB)/inc