New shared_ptr implementation

[vaxerski]

The reasoning is quite simple - this is a more useful shared_ptr implementation. Whether the impl itself is better - God knows.

I am not sure if this is a great idea either, but:

weak_ptrs got two new superpowers that the stl ones dont have:

• you can dereference a weak_ptr directly. This will obviously segfault on a nullptr deref if it's expired.
  • this is useful to avoid the .lock() hell where we are 100% sure the pointer should be valid. (and if it isn't, it should throw.)
• weak_ptrs are still valid while the SP is being destroyed.
  • reasoning: while an object (e.g. CWindow) is being destroyed, its weak_ptr self should be accessible (the sp is still alive, and so is CWindow), but it's not because by stl it's already expired (to prevent resurrection)
  • this impl solves it differently. w_p is expired, but can still be dereferenced and used. Creating s_ps is not possible anymore, though.
  • this is useful in destructors and callbacks.

review pls @outfoxxed @fufexan and everyone else.

TODO:

• Battle testing.
• Fix invalid delete

[vaxerski]

should be working. Also ran a quick test for possible leaks, doesn't seem to leak. Needs more testing, though.

[vaxerski]

thanks, cheers