Added empty-check for linkedlist
Removed unused testcase variable
Ensure that the first element points nowhere after insertion
More extensive testing for the ll insertion and deletion

We actually should test if the data is in the linked list as well as
whether it was removed after we called the appropriate remove function.
Check if the linkedlist is actually empty after insertion and deletion of the elements
removed unused variable
Fix: Use only ll functions on test_ll_insert_data
Fix: Use only ll functions in test_ll_delete_data
Fix: Use only ll functions in test_ll_insert_multiple
Fix: Use only ll functions in test_ll_delete_by_predicate
Fix for older check versions with buggy ck_assert_int_eq()
Add option DEBUG_OUTPUT
Make console spamming optional through DEBUG_OUTPUT
Merge pull request #147 from matthiasbeyer/expand-ll_tests

Expand ll tests
Merge pull request #235 from neithernut/add-build-debug_output_flag

Add build debug output flag