save_axs_table() deletes files from path

[ctslater]

I was using save_axs_table() to save the new ZTF data and used the path= argument to put it on the new disk drives. Spark then deleted everything from the path I gave it, including a bunch of unrelated directories and all the ZTF data I was trying to import.

[zecevicp]

This is how Spark's saveAsTable() method works. I added a warning note in the save_axs_table() method's documentation about this.

[ctslater]

Let's leave this open until we have more of a safeguard. I agree that it's how spark works, but I lost a few days of work to this and it could be much worse if someone specifies their home directory, for example, so I think it's a very risky thing to expose to the user.