Add noexcept to all functions it makes sense on.

[Sqeaky]

This is a bug because it leaves performance on the table and this is an enhancement because it does work now. It should be straightforward because this is a tiny library, but each function that reaches in the std library needs to check the docs that it will never throw.

If someone wants to attempt this who has never used C++11 noexept here is the cppreference docs: http://en.cppreference.com/w/cpp/language/noexcept_spec