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
> isn't return-type deduction also supported in C++11 as an extension?

Ah, yes. GCC accepts return type deduction for normal functions as an extension. However, it seems that other macros (e.g. c++11 variadic templates) are not defined with -std=gnu++03.
http://melpon.org/wandbox/permlink/LxU8OfRbucN4buru
Then, I think new macros also compliant such behaviour is the better way.

> Also, what's the practical difference between N3386 and N3638 apart from decltype(auto)?

[n3638](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3638.html) shows the change log from n3386, but I have no effective examples.
Although we can define the macro with GCC < 4.8, we might have to add a new macro (e.g. BOOST_NO_CXX14_RETURN_TYPE_DEDUCTION_N3638).