Rethink alignment specification

[ymmt2005]

Although alignas was introduced to C++11, it is limited to max_align_t length
which may be less than the CPU cache line size. The current yrmcds implementation
wrongly specify such an alignment length over the maximum. See #70 for details.

C++1z will introduce std::hardware_destructive_interference_size to avoid false
cache line sharing.

c.f. http://faithandbrave.hateblo.jp/entry/2016/07/08/174657