Reading EntityReference on open when use as a node

Read EntityReference node and add it to the SvgDocument.

```
<?xml version="1.0"?>
<svg xmlns="http://www.w3.org/2000/svg" width="800px" height="800px">
  <g>
    <rect width="200px" height="200px" fill="black" />
    <text x="100px" y="100px" font-family="Verdana" font-size="24" fill="white" text-anchor="middle">&name;</text>
  </g>
</svg>
```
.Net 3.5 Support and Marker Fixes

- 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
Marker support. perserveAspectRatio Align support
New types/converters for markers and aspect ratio
Finished aspect ratio parser
Fixed ConvertFrom for orient and aspect ratio
Merge pull request #73 from Guymestef/master

Reading EntityReference on open when use as a node
added nuspec files
Improve SVG Support: TSpans, Paths, etc.

- 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 a marker to scale with either the stroke width or the use a
custom coordinate space
- Allow gradients to reference other gradients defined later in the SVG
- Respect the font and fill styles of TextSpan elements.  Current
support is still partial.
- Fix href attribute bug on the SVG use element
Merge pull request #75 from bcbarnes-gmx/Devel

fixed up the support for markers so that they draw properly, and added support for "preserveAspectRatio" except for the 'slice' and 'defer' options.
Descendants Extension and Metadata Tweaks

- 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.
updated version to 1.7
Merging with Official Project
Merge pull request #77 from erdomke/master

.Net 3.5 Support and Rendering Improvements (Markers, TSpans, Paths, etc.)
Fixing Build Errors
Revert ".Net 3.5 Support and Rendering Improvements (Markers, TSpans, Paths, etc.)"
Merge pull request #78 from vvvv/revert-77-master

Revert ".Net 3.5 Support and Rendering Improvements (Markers, TSpans, Pa...
Merge pull request #79 from erdomke/master

.Net 3.5 Support and Rendering Improvements (Markers, TSpans, Paths, etc.) + Working Build!