add internal documentation

[amtoine]

after discussing with @stormasm a bit about the make-cache command, i thought we could add some internal documentation, not too much but just enough to make sense 😋

changelog

• rename make-cache to clean-cache-dir to hopefully make more sense
• sanitize the paths given to add-to-cache, save-cache and remove-from-cache => the paths given to them were not always sanitized, this should help make this sanitization more consistent
• add some documentation to the internal commands, for when we'll have true LSP support 😉
  • on the biggest thing is telling from the outside whether a path is sanitized or not