Add XDG path support (#476)

[taep96]

Fixes #476

Moved the .espup directory and the export file to $XDG_DATA_HOME

[SergioGasquez]

Hi! Thanks for the PR, there are some failing test though, and we would also need the esp-idf-sys follow-up PR, otherwise this would leave it on a non-working state

[taep96]

Hi! I planned to make a pr for esp-idf-sys after this one is done.

I started a review on the line causing the tests to fail. It seems to be checking whether the config location is a directory but it doesn’t exist yet; despite that it works properly on my system.

How should I deal with it?