- This will be used for TLS pages, among other things.

- Also add a missing include.

- helpful to disambiguate Kernel::Memory namespace.

Neither core nor web_services use OpenSSL nor LibreSSL.
However they need to link them as it's a requirement of httplib.
So let's declare this within httplib instead of core and web_services.

The original idea of returning pointers is that handles can be moved.
The problem is that the implementation didn't take that in mind and made
everything harder to work with. This commit drops pointer to handles and
returns the handles themselves. While it is still true that handles can
be invalidated, this way we get an old handle instead of a dangling
pointer.

This problem can be solved in the future with sparse buffers.

Removes a redundant variable that is already satisfied by the IsFull()
utility function.

Provides logical symmetry to the interface.

This doesn't modify internal state, so this can be made const.

Eliminates redundant atomic reference count increments and decrements.

Fixes broken documentation references.

Previously this was mutable even though it shouldn't be.