Modified TTaggedTextLexer to emit only first of any sequence of white space characters. Any intervening tags are ignored for this purpose so that "x <em> y </em> x" is parsed as "x <em>y </em>x". A side effect is that a text token with an empty string can be returned.
Changed TREMLReader.Parse to ignore empty text tokens received from lexer: no active text element is generated for empty string.
