[REQUEST] Set mailcap file location to $XDG_CONFIG_HOME/tuir/mailcap

Is your feature request related to a problem? Please describe.

I already had a mailcap file at $HOME/.mailcap, so I thought it was frustrating that tuir --copy-mailcap tried to overwrite that file. W3m uses an applications-specific mailcap file at $HOME/.w3m/mailcap, which I feel is a better setup.

Describe the solution you'd like

A tuir-specific mailcap file should be located at XDG_CONFIG_HOME/tuir/mailcap.

At first I thought this was would be hard to implement because mailcap.getcaps() reads from a preset list of mailcap files. However, I learned that it is possible to set the files getcaps will check using the environment variable MAILCAPS.

I've already implemented a solution in my own fork and it's been working fine for me. It still checks mailcap files at the standard locations, including $HOME/.mailcap, so tuir users won't have to move their existing mailcap file to the new location.

Additional context

As I said, I've already implemented a solution in my own fork, so I'll have a pull request available right away.

Hope to hear back from you soon! Also, thank you for adopting rtv!