std::string and shared_ptr instances are almost always passed by value

[mgerhardy]

... forcing a new allocation for each function call and for the shared_ptr an increase of the atomic value each time you pass it by value. They should almost all be passed by reference to reduce memory and atomic operations.

[phs]

Hello!

I'm always happy to look at pull requests, but unless there is a demonstrable bug I probably won't get to this myself for a while.

Hopefully the dev environment will be portable enough that, if you care to try your hand, it should not be too hard to get started.