message: find: Support `std::find_if`.
diff: #pragma once
  +#include <algorithm>
  +
  #include <elle/BoolIterator.hh>
  namespace elle
  @@ -7,8 +9,20 @@ namespace elle
  template <typename C, typename E>
  auto
  find(C& c, E const& e)
  + -> BoolIterator<decltype(c.find(e))>
  {
  auto it = c.find(e);
  return BoolIterator<decltype(it)>(it, it != c.end());
  }
  +
  + template <typename C, typename F>
  + auto
  + find(C& c, F const& f)
  + -> std::enable_if_t<
  + sizeof(decltype(f(*std::begin(c)))) >= 0,
  + BoolIterator<decltype(std::find_if(std::begin(c), std::end(c), f))>>
  + {
  + auto it = std::find_if(std::begin(c), std::end(c), f);
  + return BoolIterator<decltype(it)>(it, it != c.end());
  + }
  }
  