Fixed random segfault when circular_buffer_destroy was called in multithreading.
Created circular_buffer_clear() to clear all data in buffer.
Added circular_buffer_clear unit test.
Implemented circular_buffer_write_none unit test.
Updated circular_buffer_ends_at unit test with empty buffer scenario and additional comments.
Added additional comments to unit tests.
Removed unimplemented/redundant unit tests.
Fixed bug with boundary conditions when wrapping head and tail. Created unit test.