Set up and tear down test suite

Added

• Assert null and assert same failure message contains the pointer reference.
• A suite can have an optional set up and tear down function.

Changed

• Combine functions get_failure_count and clear_tests in function run_tests.

Improve assertion messages

Fixed

• In assertion messages, the variable name was displayed instead of the variable value.
• Fix messages of negated assertions.

Create a minimal unit framework for C

Added

• Create a test suite with test cases.
• Create a test case as function.
• Check assertions with ASSERT macros.
• Run tests with CI friendly output on console and return value.