New method of defining valid faces

[oversword]

Fixes #67 again, but better this time

This uses the new valid faces method defined in joe7575/tubelib2#8, and must be tested along with that

I have also removed the "sides" code, as it now appears in the base tubelib module, and is accessible from the tubelib2 global

[oversword]

Just noticed the changes to the way dir_to_side / side_to_dir is defined is a version-breaking change - techpack and tubelib will have to be on the latest versions or it'll crash. Happy to revert this if you'd prefer, I was just doing some cleanup of code duplication.

[oversword]

@joe7575 At this point this new feature is definitely version breaking, not sure if there's much I can do about that anymore, I could add more safety checks & duplicate the new functions across the modules if you absolutely require this to be backwards compatible

[oversword]

Ugh, I'm still seeing an issue where a destination teleporter - that does not interface with any other node - does not properly update the connection to its partner. I think this is outside the scope of the valid sides issue, all that is still required, but it does fall under this issue.

All issues regarding pushing items into teleporters are resolved, it updates correctly.

I also haven't tested this PR in terms of pulling items or stacks, will need to do that before this gets merged.

Basically, joe7575/tubelib2#8 is good and ready to go, but this one needs a little more work

[joe7575]

Very good and clean work 👍