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.

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

- 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

- 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

- 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

- 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

- 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
- Added unit test project for unit test of new functionality.

- Implemented .Net 3.5 support mostly by removing ISvgEventCaller
functionality in .Net 3.5 build
- Added ability to parse orient="auto"
- Added ability to parse colors such as rgb(#%, #%, #%)
- Fixed marker rendering implementation

https://github.com/vvvv/SVG/issues/23#issuecomment-25747963

This reverts commit 8c10c2e6.