Fix: Build infrastructure: Iteration through ary of tests
Added simple insertion test for linkedlist type
Added test for deletion
Added test for inserting/deleting multiple values
Added test for element allocation
Added test for allocating ll_element with data
Add function to cut the lowest element from a subtree
Add function for isolation of root node
Fixup documentation of isolate_root_node
Rename function cut_lowest to isolate_lowest
Fixup documentation of isolate_lowest
Extend internal documentation in isolate_root_node
Fix: Version compatible function calls

As this bullshitbuntu on the CI has only an ancient version of the check
framework in the repos, and a setup with something from the backports
seems to be more difficult than it should be, this patch fixes the tests
here to use only calls to asserts which are present in the check-version
on the CI servers.
Fixup: Rename function isolate_lowest to isolate_leftmost
Merge pull request #96 from neithernut/add-avl_internal-advl_del_prequisites

Add avl internal avl del prequisites
Enable verbosity when running tests
Merge pull request #58 from matthiasbeyer/add-ll_tests

[WIP] Add testing for linked list implementation