Added required structure to implement unit tests

Added modifications inside the main Makefile to refers the unit test Makefile.
Added separated Makefile only for compiling unit tests.
Added simple example of unit test.

Signed-off-by: Charles Oliveira <18oliveira.charles@gmail.com>
Signed-off-by: Pablo Alejandro <pabloabur@usp.br>
Signed-off-by: Rodrigo Siqueira <siqueira@ime.usp.br>

.gitignore

@@ -1,6 +1,7 @@
 *.o
 *.d
 .*.swp
+*.gch
 /.cproject
 /.project
 /.settings
@@ -27,3 +28,5 @@
 /yosys-win32-vcxsrc-*
 /yosysjs-*
 /libyosys.so
+/tests/unit/bintest/
+/tests/unit/objtest/