Add <span> tag and limited support for CSS styles to wxHTML.

Parse "style" attributes of the HTML tags and honour those of them that can be
mapped to the HTML 3 attributes.

Also add a handler for <span> tag.

Closes #10631.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64443 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -472,6 +472,7 @@ All (GUI):
 - wxGrid: add possibility to prevent resizing of individual rows/columns.
 - wxGrid: allow changing the horizontal alignment of numeric cells.
 - wxHTML: add support for table borders width (Laurent Humbertclaude).
+- wxHTML: add limited support for span elements styles (Nigel Paton).
 - Added wxMouseEventsManager.
 - Building OpenGL library is now enabled by default.
 - Fixed wxDataViewCtrl::Set{Foreground,Background}Colour().