More serialization bug fixes and better fallback for font definition
problems.

Added parameter to the SvgAttribute indicating whether the storage is
the _attribute dictionary.  If true, the output will only be serialized
only if the key is in the dictionary.  This structure is an alternate to
the SvgDefinitionDefaults class.

Revert "changed the default MatrixOrder to Prepend (instead of Append)"

changed the default MatrixOrder to Prepend (instead of Append)

fixed NullReferenceException when _styles is not set

fixed NullReferenceException in TryGetAttribute when _styles dictionary is not set to a valid reference

fixed invalid font size unit comparison

Revert "Performance Improvement"

Performance Improvement

- Because querying the Bounds property of an ISvgBoundable or
  SvgVisualElement is expensive, we introduced an ImmutableBoundable that
  is used by the SvgRenderer. This class stores the bounds of the supplied
  ISvgBoundable so that multiple queries for the bounds do not hamper
  performance when rendering.

- Converted the Bounds property on ISvgBoundable and SvgVisualElement to a
  CalculateBounds method to indicate that it is an expensive operation
  that returns a new value each time it is called.

- Removed redundant ISvgBoundable Location and Size properties.

- Fixed a bug in SvgFragment.Path property by converting it to a method that
  indicates it returns a new GraphicsPath instance when called and by
  disposing of that instance in CalculateBounds. There are many more
  instances of GraphicsPath not being disposed in the code base but we did
  not address that here.

Fix for null path

External CSS Option for SVGDocument

Initial Filter, Svg Font, and Text on a Path Support

Added External Cascading Style Sheet Option to SVGDocument.

- Improving rendering of SVG images
- Allow markers on lines, polygons, and polylines
- Implement different line joins and line caps
- Improve CSS handling

- Better parser for dealing with parsing edge cases
- Fix corner radius for rectangles
- Fix to gradients.  Most tests now pass
- Add the possibility for a fallback paint server
- Initial fixes to clipping
- Start marking passed test
- Fixes to pattern rendering

- Fixing path parsing algorithm to deal with nuanced arc cases and
hopefully improve performance
- Attempts at better memory management
- Working toward getting symbols to render correctly

- Extraction interface for SvgRenderer
- Initial support for Text on a Path
- Initial support for Svg Fonts
- Support for symbol element
- Minor bug fixes with image pattern rendering
- Additional support for Text whitespace modes

- Support of generic fonts (serif, sans-serif, monospace)
- Initial support of filters
- Fixes to gradient rendering

Bug Fixes: Remove WPF dependency
Fix compilation error after merge I also worked on:
Add support for underline and strike through
Fix whitespace handling with text rendering

- Remove WPF dependency
- Fix compilation error after merge
- Add support for underline and strike through
- Fix whitespace handling with text rendering

Initial Work on W3C Test Compliance