Add cc_check_alloc_count() function. Fixed memory leaks.

In a normal build, cc_check_alloc_count() is a no-op.  If libcoatcheck is
built with CC_COUNT_ALLOCS defined, the various cc_ memory allocation
functions in cc_memory.h will keep a global count of allocations and
deallocations and the cc_check_alloc_count() will warn if this value is not
zero when it is called.

The cc_stdio_runner_main() function calls cc_check_alloc_count() before
returning the failure count.

Fixed memory leak in cc_runner_run() by calling cc_failure_free() on any
failures generated by a test.

Fixed memory leaks in cc_assert_tests.c by freeing failures and arrays
created by tests.