Replaced printTo() with serializeJson()

* Added `serializeJson()` and `serializeJsonPretty()`
* Added `measureJson()` and `measureJsonPretty()`
* Removed `printTo()` and `prettyPrintTo()`
* Removed `measureLength()` and `measurePrettyLength()`

test/JsonSerializer/JsonArrayPretty.cpp

@@ -0,0 +1,74 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2018
+// MIT License
+
+#include <ArduinoJson.h>
+#include <catch.hpp>
+
+static void check(JsonArray& array, std::string expected) {
+  std::string actual;
+  size_t actualLen = serializeJsonPretty(array, actual);
+  size_t measuredLen = measureJsonPretty(array);
+  CHECK(actualLen == expected.size());
+  CHECK(measuredLen == expected.size());
+  REQUIRE(expected == actual);
+}
+
+TEST_CASE("serializeJsonPretty(JsonArray)") {
+  DynamicJsonArray array;
+
+  SECTION("Empty") {
+    check(array, "[]");
+  }
+
+  SECTION("OneElement") {
+    array.add(1);
+
+    check(array,
+          "[\r\n"
+          "  1\r\n"
+          "]");
+  }
+
+  SECTION("TwoElements") {
+    array.add(1);
+    array.add(2);
+
+    check(array,
+          "[\r\n"
+          "  1,\r\n"
+          "  2\r\n"
+          "]");
+  }
+
+  SECTION("EmptyNestedArrays") {
+    array.createNestedArray();
+    array.createNestedArray();
+
+    check(array,
+          "[\r\n"
+          "  [],\r\n"
+          "  []\r\n"
+          "]");
+  }
+
+  SECTION("NestedArrays") {
+    JsonArray& nested1 = array.createNestedArray();
+    nested1.add(1);
+    nested1.add(2);
+
+    JsonObject& nested2 = array.createNestedObject();
+    nested2["key"] = 3;
+
+    check(array,
+          "[\r\n"
+          "  [\r\n"
+          "    1,\r\n"
+          "    2\r\n"
+          "  ],\r\n"
+          "  {\r\n"
+          "    \"key\": 3\r\n"
+          "  }\r\n"
+          "]");
+  }
+}