Nathan Russell

E.g. in [`spp_traits.h`](https://github.com/nathan-russell/hashmap/blob/master/inst/include/hashmap/sparsepp/spp_traits.h#L54-L59) either remove completely or use a better check for C++98 mode. Currently still triggering `-Wc++11-long-long` on `r-devel-debian-clang` and `r-devel-fedora-clang`.

1. Make `boost::lexical_cast` on `Vector` equivalent to `as.character` 2. Convert `Date` and `POSIXct` vectors correctly https://github.com/nathan-russell/hashmap/blob/master/inst/include/hashmap/tools.hpp