Added support for cursormark
Disallow construction of CursorMark.
It's a value managed by Solr only, not by the client.
Added cursormark documentation
Fix some typos. Better docs
Enforce "cursor or start" constraint in the type system.
Merge CursorMark into StartOrCursor.Cursor
Update CursorMark.md
Update Querying.md
Merge branch 'cursormark'

Conflicts:
	Tests.fsx