starting to add border style structures
added border css keywords
implementing border style accessors
added initial style for borders
added border attributes to core style
adding check for border validity
implementing borders shorthand
implementing borders shorthands
implementing borders shorthands
implementing style computing for borders
added used values for borders
implemented border width used value computation
Merge branch 'debug' into borders
improved borders cascading
adding borders to layout
adding borders to layout
implemented borders in layout
Merge branch 'debug' into borders
implementing borders drawing
bug fixes for borders