Create design document to set the guidelines for handling RNDF files

[basicNew]

Some things to consider:

• The idea is to reuse the parser in gazebo and other tools. The library will most likely be implemented in C / C++.
• Consider an standalone RNDF viewer. Does it make sense to do a web viewer? The main drawback I see here is that we wouldn't be able to reuse the parser.
• RNDF files should be generated in a separate file. Then we should have a gazebo model that points to that file to import it (similar to what Gazebo does today to import e.g. collada files).
• Even though not in the near roadmap, always keep in mind that at some point we may need to move to Opendrive.
• Define interface for exporter / importer and internally for the importer (parser / visualization).

[basicNew]

Closing this one as the doc has already been created and is well-known to both parties.