PROTOCOL_VERSION, test items, MOTD fix (#18)

* Cleaned up protocol selection.

* cmake now works even if protocol option is omitted
* make now supports protocol selection
* removed PACKET_VERSION/CNPROTO_VERSION* redundancy
* ubuntu appveyor script has yet to be written
* cleaned up some trailing spaces

* Add some test items.

Ironically, this change is untested.

* [bugfix] Transmit MOTD when entering the game, not when loading screen fades.

This fixes unnecessary retransmission when /warping.

appveyor.yml

@@ -43,7 +43,7 @@ for:
                 Remove-Item "build" -Recurse
                 Write-Output "Deleted existing build folder"
             }
-            Invoke-Expression "cmake -B build -DPACKET_VERSION=$version"
+            Invoke-Expression "cmake -B build -DPROTOCOL_VERSION=$version"
             if ($LASTEXITCODE -ne "0") {
                 Write-Error "cmake generation failed for version $version" -ErrorAction Stop
             }