Organized projects using Solution Folders
NuGet: changed from MS.Bcl.immutable 1.1.29 to the new name System.Collection.Immutable 1.1.32

- note: only impacts experimental in memory db
AsyncLinq: added Distinct(), MinAsync(), MaxAsync(), ElementAtAsync(), and ElementAtOrDefaultAsync()
AsyncLinq: added some [NotNull] and cleaned up spaces
Fixed crash in FDBShell command 'count' if directory path not found