add sort support to search, add index fields command, fix error messages (#25)

TODO.md

@@ -4,8 +4,30 @@
 - Fix index names custom completion
   https://github.com/urfave/cli/issues/2332
   https://github.com/urfave/cli/issues/2333
-  
+
 - index show: add more details, see screenshots
 
 - add shard explain, aka:
   get /_cluster/allocation/explain {"index":"yourindex", "primary": true, "shard":0}
+
+
+- add validate:
+
+> GET /mock/_validate/query?rewrite=true {"from":0,"query":{"bool":{"must":[{"match_all":{}}]}},"size":20,"sort":[{"name":{"order":"desc"}}]}
+{
+  "valid": false
+}
+
+- add explain to search (maybe option -e)
+
+> GET /mock/_explain/1780043878 {"query":{"bool":{"must":[{"match_all":{}}]}}}
+{
+  "_index": "mock",
+  "_id": "1780043878",
+  "matched": true,
+  "explanation": {
+    "value": 1.0,
+    "description": "*:*",
+    "details": []
+  }
+}