Add a boost.datetime example ('chrono.cc': measure time duration).
Add a boost.datetime example ('chrono.cc': measure time duration).

jeremiedecock/snippets,jeremiedecock/snippets,jeremiedecock/snippets,jeremiedecock/snippets,jeremiedecock/snippets,jeremiedecock/snippets,jeremiedecock/snippets,jeremiedecock/snippets,jeremiedecock/snippets,jeremiedecock/snippets,jeremiedecock/snippets,jeremiedecock/snippets,jeremiedecock/snippets