Style: Consider using trailing underscores for protected/private attributes and methods in C++

Currently we follow [Google's C++ Style guide](https://google.github.io/styleguide/cppguide.html#Variable_Names) and use trailing underscores for protected/private attributes
```c++
class A {
public:
void a_method();
int a;
protected:
void b_method();
int b_;
private:
void c_method();
int c_;
};
```

I propose that we switch to using leading underscores for both attributes and methods in our C++ code base.
```c++
class A {
public:
void a_method();
int a;
protected:
void _b_method();
int _b;
private:
void _c_method();
int _c;
};
```

*Alternatives*

Use trailing underscores for both methods and attributes. This would be more C++-y and less Pythonic, but IMO less readable.