Proposal/no cxx14 macros

I also propose BOOST_RELAXED_CONSTEXPR, which will help Fusion's constexpr supports: [Test output: BP x86_64 C++11 - fusion - swap / clang-linux-3.4~c11_libc++](http://www.boost.org/development/tests/develop/developer/output/BP%20x86_64%20C++11-boost-bin-v2-libs-fusion-test-swap-test-clang-linux-3-4~c11_libc++-debug-debug-symbols-off.html)

New macros:
- BOOST_NO_CXX14_BINARY_LITERALS
- BOOST_NO_CXX14_RETURN_TYPE_DEDUCTION
- BOOST_NO_CXX14_DECLTYPE_AUTO
- BOOST_NO_CXX14_INITIALIZED_LAMBDA_CAPTURE
- BOOST_NO_CXX14_GENERIC_LAMBDAS
- BOOST_NO_CXX14_DEPRECATED_ATTRIBUTES
- BOOST_NO_CXX14_DIGIT_SEPARATOR
- BOOST_NO_CXX14_VARIABLE_TEMPLATES
- BOOST_NO_CXX14_RELAXED_CONSTEXPR
- BOOST_NO_CXX14_MEMBER_INITIALIZERS_AND_AGGREGATES
- BOOST_NO_CXX14_SIZED_DEALLOCATION
- BOOST_RELAXED_CONSTEXPR
>> Let's try to not add too many new macros please - especially as no Boost
> library needs any of these quite yet.
>
> Boost.Fusion does. There is a recent mailing list post complaining that Boost.Fusion's develop branch (which no-one should use for anything serious anyways) is broken in C++11 because it uses BOOST_CONSTEXPR to denote C++14 constexpr functions.
>
> Either Boost.Config gets a way to differentiate between C++11 and C++14 constexpr, or Boost.Fusion will need to develop its own.

We will definitely add a macro for C++14 constexpr, my comment above was 
related to different "flavors" of return type deduction.