remove unnecessary files and clean descriptions
remove parseURI helper function

remove parseURI helper function (doesn't fit the purpose of the module)
update CoAP constants to recent values

update constants to match values in coap-18, block-14 and observe-11
add optionList method to Options class
add Accept option helper properties to Options class
change observe callback to accept additional args

setObserve now accepts additional args, which are passed to observe
callback on every notification. This approach is consistent with other
Twisted callbacks.
fix bug in message retransmission
add size negotiation support for clients performing block2 requests
add size negotiation support for servers receiving block1 requests