observatory herald (#30)

* WIP: initial commit for observatory herald

* Plugin error handling refactor

* make error window non-modal

* tidy up plugin error handling

* first pass for basic herald functionality

* corrections for linux env

* Use FNV hash directly instead of managing through dictionary/index file

* resolve audio queuing issue, switch to personal NetCoreAudio fork

* merge cleanup

* add enable setting, populate defaults

* framework xml doc update

* Adjust settings, add style selection, replace locale with demonym in dropdown list.

* Test is position is on screen before saving/loading.

* use a default that's actually in the list

ObservatoryExplorer/Explorer.cs

@@ -239,7 +239,7 @@ namespace Observatory.Explorer
                 NotificationArgs args = new()
                 {
                     Title = bodyLabel + bodyAffix,
-                    TitleSsml = $"<speak version=\"1.0\" xmlns=\"\" xml:lang=\"en-US\">{bodyLabel} {spokenAffix}</speak>",
+                    TitleSsml = $"<speak version=\"1.0\" xmlns=\"http://www.w3.org/2001/10/synthesis\" xml:lang=\"en-US\"><voice name=\"\">{bodyLabel} {spokenAffix}</voice></speak>",
                     Detail = notificationDetail.ToString()
                 };