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>
```
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
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.
updated version to 1.7
Merging with Official Project