Implement unit testing (#30)

- Create `test` and `tactility-core-tests` subprojects
- Created tests for `thread.c`
- Fixed issue with thread cleanup (see what I did there? :P)
- Removed functions from `thread.h` that did not exist anymore
- Updated `ideas.md`

tests/tactility-core/CMakeLists.txt

@@ -0,0 +1,21 @@
+project(tactility-core-tests)
+
+enable_language(C CXX ASM)
+
+set(CMAKE_CXX_COMPILER g++)
+
+file(GLOB_RECURSE TEST_SOURCES ${PROJECT_SOURCE_DIR}/*.cpp)
+add_executable(tactility-core-tests EXCLUDE_FROM_ALL ${TEST_SOURCES})
+
+target_include_directories(tactility-core-tests PRIVATE
+    ${DOCTESTINC}
+)
+
+add_test(NAME tactility-core-tests
+    COMMAND tactility-core-tests
+)
+
+target_link_libraries(tactility-core-tests
+    PUBLIC tactility-core
+        freertos-kernel
+)