Move edt as part of track asset

[hzheng40]

Addresses #107

1. Added edt as part of track assets that are downloaded
2. Fixed path where maps are saved and loaded from
3. Load EDT if available instead of creating on the fly every time, should be quite a bit of speed up for set_map()
4. Added example script for creating the EDT for a track

[nandantumu]

Looks pretty good, but have a few questions

[luigiberducci]

Looks good to me.

I would integrate the creation of EDT directly into the track loading.
We can keep this as an example anyway or get rid of it.

[luigiberducci]

@hzheng40 I have added a test for a kind of corner case we discussed in the last meeting. The changes proposed should address it.

Scenario:
The EDT has been created, then the user modifies the map (e.g., add obstacles manually).
Now there is a mismatch between the map image and the EDT and the simulator will load the old EDT.

Current behavior:
The simulator will load an outdated dt.

Expected behavior:
The EDT must be recomputed and override the old one.

[luigiberducci]

a couple of changes necessary

[luigiberducci]

Suggested change

	from f110_gym.envs.track import Track
	from f1tenth_gym.envs.track import Track

[luigiberducci]

why this? it does not point to the right "maps" directory in this way

Suggested change

	map_dir = pathlib.Path(__file__).parent.parent.parent.parent.parent / "maps"
	map_dir = pathlib.Path(__file__).parent.parent.parent.parent / "maps"