fs/hash: align hashsum names and update documentation (#5339)

- Unify all hash names as lowercase alphanumerics without punctuation.
- Legacy names continue to work but disappear from docs, they can be depreciated or dropped later.
- Make rclone hashsum print supported hash list in case of wrong spelling.
- Update documentation.

Fixes #5071
Fixes #4841

docs/content/commands/rclone_hashsum.md

@@ -25,15 +25,20 @@ Run without a hash to see the list of all supported hashes, e.g.
 
     $ rclone hashsum
     Supported hashes are:
-      * MD5
-      * SHA-1
-      * DropboxHash
-      * QuickXorHash
+      * md5
+      * sha1
+      * whirlpool
+      * crc32
+      * dropbox
+      * mailru
+      * quickxor
 
 Then
 
     $ rclone hashsum MD5 remote:path
 
+Note that hash names are case insensitive.
+
 
 ```
 rclone hashsum <hash> remote:path [flags]