Add expression in. (#171)

* Add expression in.

* Add test for expression in.

MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/expressions/Expression.java

@@ -1536,6 +1536,42 @@ public class Expression {
     return at(literal(number), expression);
   }
 
+  /**
+   * Retrieves whether an item exists in an array or a substring exists in a string.
+   *
+   * @param needle     the item expression
+   * @param haystack   the array or string expression
+   * @return true if exists.
+   * @see <a href="https://www.mapbox.com/mapbox-gl-js/style-spec/#expressions-in">Style specification</a>
+   */
+  public static Expression in(@NonNull Expression needle, @NonNull Expression haystack) {
+    return new Expression("in", needle, haystack);
+  }
+
+  /**
+   * Retrieves whether an item exists in an array or a substring exists in a string.
+   *
+   * @param needle     the item expression
+   * @param haystack   the array or string expression
+   * @return true if exists.
+   * @see <a href="https://www.mapbox.com/mapbox-gl-js/style-spec/#expressions-in">Style specification</a>
+   */
+  public static Expression in(@NonNull Number needle, @NonNull Expression haystack) {
+    return new Expression("in", literal(needle), haystack);
+  }
+
+  /**
+   * Retrieves whether an item exists in an array or a substring exists in a string.
+   *
+   * @param needle     the item expression
+   * @param haystack   the array or string expression
+   * @return true if exists.
+   * @see <a href="https://www.mapbox.com/mapbox-gl-js/style-spec/#expressions-in">Style specification</a>
+   */
+  public static Expression in(@NonNull String needle, @NonNull Expression haystack) {
+    return new Expression("in", literal(needle), haystack);
+  }
+
   /**
    * Retrieves a property value from the current feature's properties,
    * or from another object if a second argument is provided.