Better logging for OmnisharpServer failures
Add GoToImplementation completer command for CSharp completer
Add GoToImplementationElseDeclaration completer command for CSharp completer
Add FindUsages completer command for CSharp completer
Remove Omnisharp server logs on shutdown if server_keep_logfiles is false
Prevent starting OmniSharp if Omnisharp has already been started
Crude razor support