node.h (Basic linked-list memory handler)

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This is a small C library that provides a new way to allocate memory, you can
use this library to allocate memory but you are now able to free all of that
memory at once. This is similar to a arena allocator in concept.

`node.h` uses a linked list where each node has a `void *` pointer. Each node of
course has a child node and that node has a child node and so on.. When you
use `node_alloc()`, the size of memory given will be `malloc()`'d to the nearest
available node, a pointer to this memory is returned. This means you can use
`node_malloc()` just like regular `malloc()`.

`node.h` also provides `node_free()` and `node_destroy()`. `node_free` takes a
`void *` pointer and will locate that memory address in the linked list, when
its found the memory will be `free()`'d, this node can of course be used
again, this saves on allocations for new nodes.

And finally `node_destroy()` will recursively free all the nodes and pointers.
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Using `node.h` means that you can allocate memory without needing to worry
about `free()`ing that memory. This is because memory allocated is held in a
linked list, this means that regardless of where we point the allocated data
we know where it is held (in the linked list).

Read `example.c` for a basic implementation.