[Feature Request] Use OS directory conventions

[pricklythorn]

Is your feature request related to a problem? Please describe.
On all platforms, tiddl's config is placed in ~/.tiddl by default, it would make more sense and align with platform conventions to place it in the OS specific directories, such as ~/.config or ~/AppData/Roaming.

Describe the solution you'd like
In tiddl/cli/const.py, there could be separate functions for getting the different types of directories, such as get_config_path() or get_cache_path(), all with a corresponding environment variable. For Linux, the XDG environment variables could be respected, the tiddl variables would take precedence over those.

Because the current directory used is ~/.tiddl, this change could only be for new users, or explicitly opted into (the CLI could move the files to the new locations).

Describe alternatives you've considered
Can't come up with any.

Additional context
These are the directories on each platform

• Linux:
  • Config: XDG_CONFIG_HOME, then ~/.config
  • Data: XDG_DATA_HOME, then ~/.local/share
  • State: XDG_STATE_HOME, then ~/.local/state
  • Cache: XDG_CACHE_HOME, then ~/.cache
• macOS:
  • Config, data, and state: ~/Library/Application Support
  • Cache: ~/Library/Caches
• Windows:
  • Config, data, and state: ~/AppData/Roaming
  • Cache: ~/AppData/Local

[oskvr37]

User already can set custom app path that changes the default ~/.tiddl directory.

[pricklythorn]

I forgot to mention, making it the default behaviour. Setting the app path will put everything in one folder instead of in their respective directories.