Linked documentation is outdated

The Readme links to kiss3d.org for documentation but the hosted API documentation there (http://kiss3d.org/doc/kiss3d/) seems to be outdated. Should better link to docs.rs (https://docs.rs/kiss3d/0.17.1/kiss3d/index.html) and maybe completely remove the documentation on the website.

Start in the README and find the link to kiss3d.org documentation. Update it to the specified docs.rs URL, then inspect the linked hosted documentation to determine whether the outdated website documentation should also be removed; done means the README points to current API documentation and no obsolete link remains.

Written by the indexing model from the issue text.