New local build setup.

Put whatever subdirectories you like in the applications directory,
they won't conflict with the upstream core-firmware git repo. The
directory structure should be, for example:

 bmp085_test/
   bmp085_test.cpp (main file)
   bmp085.cpp      (library)
   bmp085.h        (library)
   build.mk        (makefile)

Then bmp085_test/build.mk should be, for example:

 ifeq ($(APP),bmp085_test)
 INCLUDE_DIRS += applications/bmp085_test
 CPPSRC += applications/bmp085_test/bmp085_test.cpp
 CPPSRC += applications/bmp085_test/bmp085.cpp
 endif

Refer to the default tinker application for details.

When you want to compile a specific application, call make and pass in
the application's name, for example:

 make APP=bmp085_test

Or to simply compile the default tinker application, omit the APP flag,
for example:

 make clean all

If you wish to change the default application, or don't want to pass in
the APP flag each time, then edit the APP in applications/build.mk,
for example:

 APP=bmp085_test

Then just call make.