Real-time safe intra-process communication

[jackieokay]

• Implement RT allocator and incorporate into examples and demos
• Implement lock-free synchronization alternative to the mutex in publisher (intra-process_publish_mutex) Lock-free executor #77
• Extract memory allocations from take_intra_process_message and store_intra_process_message for pool alternative (solution: allocator template)
• Alternative for std::map in IntraProcessManager (solution: allocator template for stdlib data structures)
• Profiling/testing

[wjwwood]

Since intra process communication has changed a lot since this was opened, I'll close it.