Add memory allocator and a subset of smart pointers

[vbe0201]

Summary

As discussed on Discord, this Pull Request mainly adds a memory allocator which is capable of mapping and managing a given memory region and implementations for shared_ptr and unqiue_ptr.

I also made the fix_codestyle script executable under Linux and reformatted everything with Clang-Format.

Goals

• Adequate replacement for std::shared_ptr and std::unqiue_ptr.

• Free of dependencies.

• Lightweight implementation.

• Clean and fast code.

• Good documentation for Doxygen.

Limitations

• Neither the memory allocator nor the smart pointers can be considered thread-safe.

  • Can be resolved by using a hs::os::Mutex.

• No support for heap allocations.

• No implementation of weak_ptr as I didn't consider it necessary.

  • If there's a demand, I can add it.

• Only a subset of the smart pointers is actually implemented.

  • The implementations can be extended if necessary.

[Kaenbyo]

For reference:

We now have a shared_ptr/unique_ptr implementation that differ from the std counterpart. This is mainly because we don't follow the allocator_traits requirements.

I also rewrote the memory allocator to use a simple free list (this still uses a first fit algorithm but I guess it's clearly enough for now).

The doc still need to be updated and some small optimization can be done on the free list fragmentation.