add DELETE options _mapping

Several mappings can be deleted at once by defining several indices and types with

`[DELETE] /{index}/{type}`

`[DELETE] /{index}/{type}/_mapping`

`[DELETE] /{index}/_mapping/{type}`

where

`index= * | _all | glob pattern | name1, name2, …`

`type= * | _all | glob pattern | name1, name2, …`

Alternatively, the keyword `_mapings` can be used.

see roadmap issue elastic#4071

docs/reference/indices/delete-mapping.asciidoc

@@ -1,8 +1,25 @@
 [[indices-delete-mapping]]
 == Delete Mapping
 
-Allow to delete a mapping (type) along with its data. The REST endpoint
-is `/{index}/{type}` with `DELETE` method.
+Allow to delete a mapping (type) along with its data. The REST endpoints are
+
+[source,js]
+--------------------------------------------------
+
+[DELETE] /{index}/{type}        
+    
+[DELETE] /{index}/{type}/_mapping      
+
+[DELETE] /{index}/_mapping/{type}  
+
+--------------------------------------------------
+
+where
+
+[horizontal]
+
+`index`::  `* | _all | glob pattern | name1, name2, …` 
+`type`::  `* | _all | glob pattern | name1, name2, …` 
 
 Note, most times, it make more sense to reindex the data into a fresh
 index compared to delete large chunks of it.

rest-api-spec/api/indices.delete_mapping.json

@@ -4,7 +4,7 @@
     "methods": ["DELETE"],
     "url": {
       "path": "/{index}/{type}/_mapping",
-      "paths": ["/{index}/{type}/_mapping", "/{index}/{type}"],
+      "paths": ["/{index}/{type}/_mapping", "/{index}/{type}", "/{index}/_mapping/{type}", "/{index}/{type}/_mappings", "/{index}/_mappings/{type}"],
       "parts": {
         "index": {
           "type" : "list",