Use relative paths in the Makefile for all assets
Use relative paths in the Makefile for all assets

For nica to be embedded in another project as a submodule or similar,
it would no longer be in the top source directory. To make this more
trivial, while allowing nica to continue to develop as a first class
library with it's own build system, we use relative pathing to enable
projects to add libnica to it's SUBDIRS in autotools.

Signed-off-by: Ikey Doherty <15e2f59c60e9d84348e78a87e24660774f739add@intel.com>

ikeydoherty/libnica,ikeydoherty/libthingamabob,ikeydoherty/libthingamabob,ikeydoherty/libthingamabob,ikeydoherty/libnica,ikeydoherty/libnica