Make height unsigned
Make documentation of member ll apply to 80c rule

The line was too long because of the extra intend added when changing
the type of the member "height".
Modify getter return type
Store number of nodes of a subtree in the root node
Add inlined getter for the node count of a subtree
Look for doxygen
Fixed typo in main gitignore
Add gitignore for documentation
Ingore stamp files used for trackign targets
Add CMakeLists file for building the doxygen doc
Ultimately add documentation target to project

...by including the ./doc subdirectory
Merge pull request #70 from neithernut/add-build_env-doc

Add build env doc
Merge pull request #73 from neithernut/add-node_cnt

Add node cnt
We actually should search with the hash here
Added implementation for avl_find()
Merge pull request #75 from matthiasbeyer/implement-avl_find

Implement avl find
Add declaration and stubs for rotations
Add declaration of node metadata regeneration func

The function declared in this commit will regenerate a node's metadata,
e.g. it's height and the node count.
Add implementation of left-rotation
Add implementation of right-rotation