More reconstruct dir struct to modulized boost's one.

Signed-off-by: Kohei Takahashi <flast@flast.jp>
More compliant original Range's documentation style

  * algorithm_ext/fused_for_each.qbk
  * ranges/directory_range.qbk
  * ranges/iteration.qbk
  * ranges/recursive_directory_range.qbk
  * ranges/single.qbk

Signed-off-by: Kohei Takahashi <flast@flast.jp>