* Fixed an indexOutOfRange warning when creating coap requests
because the first addOption() call was calling
m_options.insert(1) on an empty list.
* Old code was appending multiple UDP datagrams to a single big Coap
message, however, Coap is specified to only send s single datagram
per message. The datagram length specifies the payload size.
* some boolean member variables weren't initialized which resulted in
occational wrong flags.
* Parsing had issues with determining the option length in some occations
and also would crash when receiving coap messages without any options
or payload. To get rid of the complex and erraneous index calculations,
the entire package parsing is now using a DataStream.
(This makes it work with Shelly devices)
