Rewerite and revert some code that this library can be built in pre-C++11 and C++11 env.
Main Change List:
1. using -> typedef
2. not using auto & decltype
3. not using raw string literals
4. ..., other c++11 features will be chosen to compile, depending on env.
CPPTL support is no longer relevant to JsonCpp, and can be removed from
the library. This patch removes all mentions of CPPTL, by removing all
definitions and code sections conditionally compiled only when JsonCpp
is used with CPPTL. Include guards are also renamed to not refer to
CPPTL where appropriate.
This patch fixes a build issue on CMake, presumably due to the new glibc
having a features.h include file. This patch renames our features.h file
to avoid a name collision.