use 'default' consistently.

README.md

@@ -172,10 +172,10 @@ The "perfield" option lets you use a different analyzer for different fields and
 perfield:{field_name:"analyzer_name"}
 </pre>
 
-Unless overridden, any field name not specified will be handled by the standard analyzer. To change the default, use the special _default field name;
+Unless overridden, any field name not specified will be handled by the standard analyzer. To change the default, use the special default field name;
 
 <pre>
-perfield:{_default:"keyword"}
+perfield:{default:"keyword"}
 </pre>
 
 <h3>The Document class</h3>

src/main/java/com/github/rnewson/couchdb/lucene/util/Analyzers.java

@@ -83,11 +83,11 @@ public Analyzer newAnalyzer(final String args) {
         @Override
         public Analyzer newAnalyzer(final String args) {
             final JSONObject json = JSONObject.fromObject(args == null ? "{}" : args);
-            final Analyzer defaultAnalyzer = Analyzers.getAnalyzer(json.optString("_default", "standard"));
+            final Analyzer defaultAnalyzer = Analyzers.getAnalyzer(json.optString(Constants.DEFAULT_FIELD, "standard"));
             final PerFieldAnalyzerWrapper result = new PerFieldAnalyzerWrapper(defaultAnalyzer);
             for (final Object obj : json.keySet()) {
                 final String key = obj.toString();
-                if ("_default".equals(key))
+                if (Constants.DEFAULT_FIELD.equals(key))
                     continue;
                 result.addAnalyzer(key, Analyzers.getAnalyzer(json.getString(key)));
             }