add T& front() and void pop() capabilities to spsc_queue
spsc_queue.hpp: slightly improved comments
spsc_queue: add assert read_available > 0 to front()
spsc_queue: implement pop() in terms of consume_one(noop) instead of dedicated method
spsc_queue: remove unused delete_range
spsc_queue: non-const T& front() added and tested
Merge pull request #4 from erenon/devel_spsc_queue_front_pop

add T& front() and void pop() capabilities to spsc_queue