add noexcept cpp generator option

The C++11 standard has deprecated the usage of throw() to express exceptions,so to avoid warnings from the compiler,I think this option is useful.

I have a pull request in github,this issue is created to track it.

Some questions remain:

1.Should we change the runtime c++ library to use BOOST_NOEXCEPT_OR_NOTHROW?

2.Should we add an control option to enable all c++11 options like moveable_types .etc?

3.Should we begin to support C+17 features? I think std::optional should be used to implement optional keyword,but this is clearly an API breaking change,so we need an c+17 control option.