Compiling with clang and gcc with -Wshadow
See issue #17

Somewhere along the way we've also broken our ability to compile with GCC 4.7.3.  We'll have to decide if we care about
supporting 4.7.3 or not.  The changes that break this are:

-there is no emplace in std::map (or related) in 4.7.3
-there are some enable_ifs in rapidjson's writer.h that are always false (which is fine), but
GCC 4.7.3 doesn't like this