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.

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

- 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.

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

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

- Adding W3C test cases and a test fixture
- Fixed support for CSS stylesheets (particularly when class names are
referenced)
- Refactoring unit calculations so that percentages and fractions
calculate more accurately
- SvgImage:
- Support PreserveAspectRatio attribute
- Support for referencing svg images
- Refactored text rendering to use the AttributeCollection inheritance
scheme
- Initial attempt at 'ex' unit support
- Added support for system color names
- Changed parsing of entities to support XML entities
- Supporting loading of a svg document directly from a XmlDocument with
requiring serializing the document as a string first.
- ...

- Very initial support of CSS stylesheets in the SVG via including the
ExCss and Fizzler libraries
- Bug fixes with path rendering
- Improvements to the API for loading an SVG file

- Begin allowing character positioning within a text element
- Start fixing bugs with linear gradients

- Support more font styles
- Fix problems with parsing 'em' svg units introduced by trying to parse
2e-5 double formats
- Move font properties to SvgVisualElement class as grouping elements
can also contain them
- Properly inherit font properties via the parent list
- Properly handle tspan offsets
- Support for .Net 3.5

GDI Pen was crashing with some bad (Adobe Illustrator) data that had: stroke-dasharray="10,10,0"

- Implemented .Net 3.5 support mostly by removing ISvgEventCaller
functionality in .Net 3.5 build
- Added ability to parse colors such as rgb(#%, #%, #%)
- Fix issues with calculating the next coordinate after a close figure
and a relative move
- Allow the std. deviation in a gaussian blur to be a float.
- Allow "none" for a unit collection
- Allow gradients to reference other gradients defined later in the SVG
- Fix href attribute bug on the SVG use element
- Adding a descendants convenience methods (similar to the Xml to Linq
API)
- Removed non-functional property from the SvgDescription class to
encourage use of the Content property instead

-Fixes issues with colors not parsing correctly. Saving an SvgDocument
resulted in RGB color values being converted to well known color names.

-Compile regex statements to improve performance.

-Make rendering a document threadsafe.

Add support for unknown svg element and non svg element: useful for not removing unknown xml tag from document when loading a file