Add Unity-based unit test infrastructure (Phase 1 — 117 tests) (#177)

Introduced new system for unit tests based on the Unity framework.

Added tests for some of the simple functions in four different files.

CMakeLists.txt

@@ -400,6 +400,7 @@ add_executable(circle ${SRC_FILES})
 target_link_libraries(circle ${EXTRA_LIBS})
 
 add_subdirectory(src/util)
+add_subdirectory(tests)
 
 if (MEMORY_DEBUG)
     message(STATUS "MEMORY_DEBUG is activated, setting up zmalloc")