enhancement (2/2): improve docs and clean-up code

[4ndrelim]

Refined almost all data structures and half of the algorithms folder. The clean-up is bigger and taking longer than expected. We will defer the following to the 3rd PR (or stand-alone):

1. Sorting algorithms
2. Fenwick trees implementation
3. B-tree refinement
4. Graph algorithms (Dijkstra, Floyd-Warshall)
5. DAGs implementation
6. MSTs
7. Orthogonal Range Searching review