Rename three commands, deprecate their old names (#887)

The following commands have been renamed to better describe their
function and avoid confusion.
:VimwikiDeleteLink → :VimwikiDeletePage
:VimwikiRenameLink → :VimwikiRenamePage
:VimwikiGenerateTags → :VimwikiGenerateTagLinks (was already renamed in 3b5537f)

Calling the old commands still works but displays a warning message.

doc/vimwiki.txt

@@ -387,13 +387,13 @@ MAP                MODE
 
                                                           *vimwiki_<Leader>wd*
 <Leader>wd         n    Delete wiki page you are in.
-                        Maps to |:VimwikiDeleteLink|.
-                        Remap command: `<Plug>VimwikiDeleteLink`
+                        Maps to |:VimwikiDeleteFile|.
+                        Remap command: `<Plug>VimwikiDeleteFile`
 
                                                           *vimwiki_<Leader>wr*
 <Leader>wr         n    Rename wiki page you are in.
-                        Maps to |:VimwikiRenameLink|.
-                        Remap command: `<Plug>VimwikiRenameLink`
+                        Maps to |:VimwikiRenameFile|.
+                        Remap command: `<Plug>VimwikiRenameFile`
 
                                                                    *vimwiki_=*
 =                  n    Add header level. Create if needed.
@@ -793,10 +793,10 @@ Vimwiki file.
     Supports |cmdline-completion| for link name. If name is not specified, a
     prompt will be shown.
 
-*:VimwikiDeleteLink*
+*:VimwikiDeleteFile*
     Delete the wiki page you are in.
 
-*:VimwikiRenameLink*
+*:VimwikiRenameFile*
     Rename the wiki page you are in.
 
 *:VimwikiNextTask*
@@ -3506,7 +3506,7 @@ https://github.com/vimwiki-backup/vimwiki/issues.
 2.5 (in progress)~
 
 New:~
-    * PR #787: |:VimwikiRenameLink| works for all directories: even
+    * PR #787: |:VimwikiRenameFile| works for all directories: even
       wiki_root/diary/2019-12-11.md if current file is wiki_root/dir1/file.md.
     * Issue #764: fenced code blocks are properly supported for markdown
       syntax i.e. more than 3 backticks, adds tilde support.
@@ -3576,6 +3576,11 @@ New:~
     * PR #857: Make default template responsive
     * PR #879: Generate links when diary & wiki dir are the same
 
+Changed:~
+    * Issue #796: Rename |:VimwikiGenerateTags| to |:VimwikiGenerateTagLinks|
+    * Issue #638: Rename |:VimwikiDeleteLink| to |:VimwikiDeleteFile|
+    * Issue #638: Rename |:VimwikiRenameLink| to |:VimwikiRenameFile|
+
 Removed:~
     * PR #698: Remove awa check triggering silent file edits.
     * Options g:vimwiki_use_mouse and g:vimwiki_table_mappings. These are
@@ -3585,7 +3590,6 @@ Removed:~
 
 Fixed:~
     * Issue #90: VimwikiRenameLink doesn't update links in diary.
-    * Issue #796: Rename |:VimwikiGenerateTags| to |:VimwikiGenerateTagLinks|
     * Issue #790: Allow tags before a header with markdown syntax.
     * Issue #779: Vimwiki tags file meets ctags standard.
     * Issue #781: Compatablity fixes for older versions of Vim.