Add figure visualising hierarchical merges
Add figure visualising a single merge
Add explanation of bit counting algorithm
Merge pull request #115 from neithernut/add-paper-bit_counting_algo

Add paper bit counting algo
Removed predicate (and predicate type, which becomes useless)
Updated documentation for the avl_del() function
Fix typo
Added argument for element to compare against when removing
Merge pull request #111 from matthiasbeyer/adapt-avl_del

Adapt avl del