rename exercises and reorganize repository structure

[arcibyte]

Currently, the exercises do not use their actual names, and the repository structure could be improved

this issue serves as a reminder to perform a general clean-up of the repository in order to make it clearer, more consistent, and easier to maintain

tasks:

• rename exercises using their actual names (according to the original problem description)
• group exercises under the correct platform and topic where applicable
• remove or refactor ambiguous or misnamed files
• btw, update the documentation