Pre-release: open-dis-rust v0.1.0-alpha.8

This is the second pre-release of the day! With this publication, the Logistics family of PDUs has been completed. Now, only 17 PDUs remain. In reviewing the README within the source tree, I realized that I had two PDU types listed that actually do not exist within the standard. I was using the Open DIS C++ library as a reference originally, and it, too, referenced PDUs that did not exist in the IEEE 1278.1 standard. So, having removed those errors, there are now only 17 PDUs left to implement. The remaining PDUs are primarily members of the Entity Management and Synthetic Environment protocol families.