Introduces wrappers around memory allocation functions in `memory.h`
that should be used instead of the standard C ones.
These never return NULL and, with the exception of `mem_realloc()`,
zero-initialize the allocated memory like `calloc()` does.
All allocations made with the memory.h API must be deallocated with
`mem_free()`. Although standard `free()` will work on some platforms,
it's not portable (currently it won't work on Windows). Likewise,
`mem_free()` must not be used to free foreign allocations.
The standard C allocation functions are now diagnosed as deprecated.
They are, however, available with the `libc_` prefix in case interfacing
with foreign APIs is required. So far they are only used to implement
`memory.h`.
Perhaps the most important change is the introduction of the `ALLOC()`,
`ALLOC_ARRAY()`, and `ALLOC_FLEX()` macros. They take a type as a
parameter, and allocate enough memory with the correct alignment for
that type. That includes overaligned types as well. In most
circumstances you should prefer to use these macros. See the `memory.h`
header for some usage examples.
