Added synchronized
Without this it might happen that the childNodes are enumerated while being modified potentially causing an exception. #335
Removed ancient test code that messed up the position of an iframe video
added sizing info to content view docs
set layerClass of DTAttributedLabel to CALayer
Usually labels would be relatively small, less than a screen full and so we can set the layer class to draw synchronously.
Removed empty file group
Added ability for DTAttributedLabel to sizeToFit to content

- Added intrinsicContentFrame to DTCoreTextLayoutFrame to return the actually used width by the layout
- Removed sizeToFit on DTAttributedLabel because superclass sizeToFit should work as well
- sizeToFit calls intrinsicContentSize. For Labels this is same as intrinsicContentFrame, for content views - which are meant to be used inside the scrolling DTAttributedTextView - the width of the bounds is used.

If you want to shrink a DTAttributedLabel to fit the contents, call sizeToFit.
If you want to know what the actual size used up by the layouted text then call [_attributedTextContentView.layoutFrame intrinsicContentFrame].size