Feature request: another set of add_xxx functions

Is it possible to have another set of add_xxx functions like:
```
bool add_ring (const void* vertices, int stride, int num_vertices, polygon_type p_type);
```
The main purpose of this is perf gain due to lack of data conversion.
I think people that write real time applications (ex.: game developers) will be grateful for this.

No files or tests are named. Start by locating the existing add_xxx entry points and the data-conversion path, then determine how a strided vertex buffer and polygon_type would fit the public API. Done means the requested overloads accept the stated inputs without conversion and preserve the existing geometry-operation behavior.

Written by the indexing model from the issue text.