Update the documentation's changelog page
Update the documentation's changelog page

Cleanup the links and add information:
- Mention the 128-bit integers support for counting_sorter
- Mention the conditional std::mem_fn extended support
- Mention the condition improvements brought by assumptions

[ci skip]

Morwenn/cpp-sort,Morwenn/cpp-sort,Morwenn/cpp-sort,Morwenn/cpp-sort