#164 TClipboard enhancements

[Vidar Hasfjord]

Using the clipboard is hard. Just copying a string to the clipboard requires lots of careful code (see Exceptions and OWLNext | Expect an exception - write exception-safe code). Copying and pasting a string to and from the clipboard should be easy. For this reason, I propose adding TClipboard::Copy (const tstring_view&) and TClipboard::PasteString() const -> tstring.

[Vidar Hasfjord]

The proposed new functions TClipboard::Copy and PasteString were added in [r5154]. The documentation for TClipboard::SetClipboardData was improved in [r5153].

These changes were merged into Owlet in [r5155].