fix: unambiguous repo key names, clearer config and key names, and a newer lazysecrets's files no longer stop an older one (#66)

Changes that would break configs or links once people use lazysecrets, made while nobody does yet.

- **Repo key names**: a dot or bracket inside a key is escaped (`app\.name`), so links to it resolve to that key and not to `app` → `name`. Dotenv files are flat, so their names stay as they are.
- **Config**: `updates.updateSources` is now `updates.sources`. A negative provider timeout, or `--timeout` of 0 or less, is an error instead of making every request fail.
- **Keybindings**: `lists.share` is now `lists.copyLink`, `lists.search` is `lists.goTo` and `lists.enter` is `lists.open`, matching what they do.
- **Version skew**, e.g. a lazysecrets.nvim theme file made for a newer lazysecrets:
  - an unknown theme role is skipped with a warning instead of stopping startup;
  - a state file from a newer version is read but not saved to, with a warning;
  - a link with an unknown provider suggests `lazysecrets update`.

Reviewed-on: #66
Co-authored-by: Karl-Einar Bergstrøm <karl-einarb@outlook.com>

internal/ref/ref.go

@@ -310,7 +310,7 @@ func parseLink(s string) (Ref, error) {
 		}
 
 	default:
-		return Ref{}, fmt.Errorf("unknown provider %q in link", u.Host)
+		return Ref{}, fmt.Errorf("unknown provider %q in link: a newer lazysecrets may know it (lazysecrets update)", u.Host)
 	}
 	return r, nil
 }