rclone special remote

Added rclone special remote, which can be used without needing to install
the git-annex-remote-rclone program. This needs a new version of rclone,
which supports "rclone gitannex".

This is implemented as a variant of an external special remote, that
runs "rclone gitannex" instead of the usual git-annex-remote- command.
Parameterized Remote.External to support that.

Sponsored-by: Luke T. Shumaker on Patreon

doc/git-annex.mdwn

@@ -1794,6 +1794,11 @@ Remotes are configured using these settings in `.git/config`.
   Used to identify Amazon Glacier special remotes.
   Normally this is automatically set up by `git annex initremote`.
 
+* `remote.<name>.annex-rclone`
+
+  Used to identify rclone special remotes.
+  Normally this is automatically set up by `git annex initremote`.
+
 * `remote.<name>.annex-web`
 
   Used to identify web special remotes.
@@ -1832,7 +1837,7 @@ Remotes are configured using these settings in `.git/config`.
 
 * `remote.<name>.annex-externaltype`
 
-  Used external special remotes to record the type of the remote.
+  Used by external special remotes to record the type of the remote.
 
   Eg, if this is set to "foo", git-annex will run a "git-annex-remote-foo"
   program to communicate with the external special remote.

doc/special_remotes.mdwn

@@ -26,6 +26,7 @@ the git history is not stored in them.
 * [[git]]
 * [[httpalso]]
 * [[borg]]
+* [[rclone]]
 
 The above special remotes are built into git-annex, and can be used
 to tie git-annex into many cloud services.

doc/special_remotes/rclone.mdwn

@@ -26,12 +26,12 @@ the time of writing, this includes the following services:
 
 That list is regularly expanding. 
 
-git-annex supports all of those through
-the use of the [rclone special remote](https://github.com/DanielDent/git-annex-remote-rclone).
+There are two ways to use rclone as a git-annex special remote.
 
-Alternatively, rclone recently gained support for being used as a special
-remote on its own, without needing installation of the above program.
-For documentation on using rclone that way, see the output of
-`rclone gitannex -h` or [here](//github.com/rclone/rclone/blob/master/cmd/gitannex/gitannex.md).
+1. Install [git-annex-remote-rclone](https://github.com/DanielDent/git-annex-remote-rclone).
+   This will work with any versions of rclone and git-annex.
+2. With a recent version of rclone and git-annex, it is not necessary to
+   install anything else, just use `git-annex initremote type=rclone ...`
 
-See their documentation for more concrete examples.
+   For documentation on using rclone that way, see the output of
+   `rclone gitannex -h` or [here](https://github.com/rclone/rclone/blob/master/cmd/gitannex/gitannex.md).

doc/todo/external_special_remotes_not_using_git-annex-remote_in_name.mdwn

@@ -44,3 +44,5 @@ a wrapper around the external special remote, that makes it use
 > I feel that the simplicity of the type=rclone config will pay off in the
 > long term, vs short term complication for probably a small subset of users
 > who somehow can upgrade rclone but can't upgrade git-annex. --[[Joey]]
+
+> > [[done]]