Add support for predefined language specific stopwords

Author: Daniel Silva

src/Nest/Domain/Analysis/TokenFilter/StopTokenFilter.cs

@@ -23,7 +23,7 @@ public StopTokenFilter() : base("stop")
         public string StopwordsPath { get; set; }
 
         [JsonProperty("stopwords")]
-        public IEnumerable<string> Stopwords { get; set; }
+        public object Stopwords { get; set; }
 
 		[JsonProperty("remove_trailing")]
 		public bool? RemoveTrailing { get; set; }

src/Tests/Nest.Tests.Unit/Core/Indices/Analysis/TokenFilters/TestStopTokenFilterWithArray.json

@@ -0,0 +1,14 @@
+{
+  "settings": {
+    "index": {
+      "analysis": {
+        "filter": {
+          "my_stop": {
+            "type": "stop",
+            "stopwords": [ "and", "is", "the" ]            
+          }
+        }
+      }
+    }
+  }
+}

src/Tests/Nest.Tests.Unit/Core/Indices/Analysis/TokenFilters/TestStopTokenFilterWithPredefinedLanguageList.json

@@ -0,0 +1,15 @@
+{
+  "settings": {
+    "index": {
+      "analysis": {
+        "filter": {
+          "my_stop": {
+            "type": "stop",
+            "stopwords": "_english_"            
+          }
+        }
+      }
+    }
+  }
+}
+

src/Tests/Nest.Tests.Unit/Core/Indices/Analysis/TokenFilters/TokenFilterTests.cs

@@ -0,0 +1,43 @@
+using Nest.Tests.Unit.Core.Indices.Analysis.Tokenizers;
+using NUnit.Framework;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Nest.Tests.Unit.Core.Indices.Analysis.TokenFilters
+{
+	[TestFixture]
+	public class TokenFilterTests : BaseAnalysisTests
+	{
+		[Test]
+		public void TestStopTokenFilterWithArray()
+		{
+			var result = this.Analysis(a => a
+				.TokenFilters(t => t
+					.Add("my_stop", new StopTokenFilter
+					{
+						Stopwords = new string[] { "and", "is", "the" }
+					})
+				)
+			);
+			this.JsonEquals(result.ConnectionStatus.Request, MethodInfo.GetCurrentMethod());
+		}
+
+		[Test]
+		public void TestStopTokenFilterWithPredefinedLanguageList()
+		{
+			var result = this.Analysis(a => a
+				.TokenFilters(t => t
+					.Add("my_stop", new StopTokenFilter
+					{
+						Stopwords = "_english_"
+					})
+				)
+			);
+			this.JsonEquals(result.ConnectionStatus.Request, MethodInfo.GetCurrentMethod());
+		}
+	}
+}