Recycling Code Symbols

This is a full set of recycling symbols for integration into your projects. There's one for each common type of filament used in 3D printing, with the code for that type according to the [Wikipedia article on recycling codes](https://en.wikipedia.org/wiki/Recycling_codes).

These symbols can be included on any item you print, as either a positive or negative imprint, depending on your preference.

This actually is derived from a Tinkercad user whose identity I've forgotten, and I made the mistake of not writing it down. (It was just one symbol, which at the time gave the wrong number for the type of plastic it cited.) If that user steps forward, I'll happily give proper credit for the work, since I would've had an incredibly hard time making the recycling triangle.

REMINDER: Before you put any plastic into your recycling bin, check to be sure that your local recycler can accept that type. (The higher the number, the less likely it is that they can take it.)