config: FilenameAttribute doesn't handle quotes well

[dgw]

Description

If the value of a FilenameAttribute set in the config file is quoted, it silently creates a mess.

Reproduction steps

1. Set core.logdir = "/path/to/logs"
2. Run Sopel
3. Sopel quietly creates a silly directory tree inside $HOMEDIR:

$ tree ~/.sopel
/home/dgw/.sopel
├── "
│   └── path
│       └── to
│           └── logs"
│               ├── default.error.log
│               ├── default.exceptions.log
│               ├── default.raw.log
│               └── default.sopel.log
...

Expected behavior

Even though quotes aren't required in Sopel's config file, they should be sensibly handled.

Environment

• Sopel .version: current master, aca1055
• Sopel installed via: -e . @ above commit
• Python version: 3.8, 3.9
• Operating system: Ubuntu 20.04 (WSL)

Notes

This is a leftover todo from #1959, where I updated the docs but didn't make any code changes related to this.

[half-duplex]

Can we just switch to TOML >.>

[dgw]

Definitely not for 8.0.

[Exirel]

As written in the doc:

Quoting a value unnecessarily can lead to unexpected behavior such as an absolute pathname being interpreted as relative to Sopel’s home directory.

[dgw]

Yes @Exirel, that's what I added in #1959. But in the interest of user-friendliness (Sopel is supposed to be "simple", remember) I think we should add sensible behavior like stripping quotes (and logging a warning), unless there are reasonable use cases where someone might intentionally want a folder named ".