Completly revised version, added ESP32 support.

This version is improved by many new functions. By implementing an own buffer management the RingBuffer extenstion is no longer neccessary. Now the buffer size can be changed also at runtime. The global object SerialAndTelnet was removed. Now you have to define it in your sketch, but now it is possible to use more than one instance of TelnetSpy (with different port numbers) and you can create the TelnetSpy object(s) dynamically when you need them. Read the README.md for all new features.