Replaced printTo() with serializeJson()

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

test/JsonSerializer/CMakeLists.txt

@@ -0,0 +1,14 @@
+# ArduinoJson - arduinojson.org
+# Copyright Benoit Blanchon 2014-2018
+# MIT License
+
+add_executable(JsonSerializerTests
+	JsonArray.cpp
+	JsonArrayPretty.cpp
+	JsonObject.cpp
+	JsonObjectPretty.cpp
+	JsonVariant.cpp
+)
+
+target_link_libraries(JsonSerializerTests catch)
+add_test(JsonSerializer JsonSerializerTests)