type erasure: another failed attempt to make s1 | s2 work
doc: manual backbone added
let tasks own input queue through unique_ptr, queue_[back|front] holds pointer only
API doc improved
queue_front: T pull() and pull(T&) removed, bool wait_pull(T&) added instead
queue.hpp: api doc added
Merge branch 'master' into type_erasure
type_erasure: drop boost.type_erasure, use custom solution instead, all tests pass. segment: use t_e interface, clone() methods added