* Rename Publish-EchoArgs to Publish-PSTestTools so it can be used
for other tools as well in the future
* Publish EchoArgs to the bin directory instead of run to match
convention
* Add source URL to EchoArgs header comment
* Use wildcard of "*.nuget.props" to match
"test/csharp/csharp.nuget.props" in .gitignore