C++14 Refactoring

[rchen20]

Now that we require C++14, we should probably update the code to reflect the niceties which come with it. Please add items to this list of code that we can fix/simplify with 14 features.

• [ ] Remove trailing return types.
• [ ] Generic lambdas (use auto in the parameter list of lambdas to pass in any type).
• [ ] decltype(auto) to preserve cv-qualifiers.