Parse the client request

[khklau]

Determine the protocol between the tile client & server and parse the client request.

[khklau]

Initial implementation of the Request struct has been added. This struct contains a MemoryPool member field, but this might turn out to be unnecessary. Any temporary usage of a heap within a hook callback can be handled by a Box backed by the global system allocator.

Any request related data that needs to be persisted between hook callbacks should be stored in and owned by the Request struct. This will ensure that Request and all request related data have the same lifetime and are dropped together.