MONGO_INITIALIZER has some unnecessary API complexity.

We don't need:
MONGO_INITIALIZER_WITH_PREREQUISITES
MONGO_INITIALIZER_GENERAL.

`MONGO_INITIALIZER` can instead take a name and 2 optional parameters.

MONGO_INITIALIZER(name)
MONGO_INITIALIZER(name,prereqs)
MONGO_INITIALIZER(name,prereqs,dependents)

The preprocessor can handle this with a `_VA_ARGS_` arity selector idiom.

We do not need the make_string_vector.h,cpp files at all.
We can remove parens from prereqs and dependents preprocessor-tuples with the preprocessor, and rely on vector<string> to brace-init in place.
This would eliminate the need to have the primitive NULL-terminated va_arg list API.

We can just have the MONGO_INITIALIZER macro directly create `vector<string>` to give the registration API as temporaries and we can more gracefully handle empty lists as () instead of (NULL). At that point we don't need the MONGO_NO_PREREQUISITES or MONGO_NO_DEPENDENTS macros because the `()` is easier to remember than `(NULL)`.