Unit Calculation: add spaces between operatores, remove obsolete default branch in switch statement.
bug fix #338

Fix issue with percentage unit in "stroke-width", now taken from the viewbox width/height normalised diagonale for x/y elements e.g. circle
Test images and svg under #338

- fixes #58

- could break the functionality if writing is not possible in root
- see #372

Fix Issue #385, using TextBounds.Width rather than path bounds to ensure proper font alignment for "middle" and "end" - see also "text-align-03-b"

- added "stroke-dashoffset" support
- added "painting-stroke-04-t" to "PassingTests" (csv/txt)
- fixes #388 

- see #384

- added a few of them to passing image comparson tests

- added image broken by regression to tests (__Flag_of_the_United_States)
- added some passing issue specific tests to image comparison tests

- first try for a matching comparison test
- compares down-scaled gray-scale images pixel-wise
- see #378

See ExCSS pull request #62: https://github.com/TylerBrinks/ExCSS/pull/62

- found by @Seairth
- fixes #108

- ignore elements with recursive references
- fixes stack overflow for test image struct-use-12-f.svg

- Catch exceptions in event handler.

- originally provided by @ssteiger in #316

- fixes TestPrivateFront unit test (threw exception because the image
  had zero size, as the only element is a "use" element)

- vertical graphics context resolution has been used incosistently which leads to wrongly positioned texts when printing

- ignore textLength attribute if X attribute is list
- add test images

- fixed a few other tests by using the Svg DTD Resolver to avoid web requests

- suppress warning CS1591: Missing XML comment for publicly visible type or member
  to avoid to overflow the build log with warnings
- fixed the rest of the documentation warnings in SVG project
- ignore all failing tests for the time being

- Fix: adjustment is wrong in lengthAdjust='spacingAndGlyphs'.
- Add test images.

fixed SvgAttrribute reflection for .net core. (i guess Equals() function is called instead of Match() on this platform?)

In <image> element, preserveAspectRatio attribute default value is 'xMidYMid meet'.

https://www.w3.org/TR/SVG11/coords.html#PreserveAspectRatioAttribute

# image opacity fix

Updated threading tests to use the resource file, updated the file loader in the test helper to be flagged as obsolete and changed the working of the multi-threading fail test since this is not always failing with the error while processing the SVG. If it's not failing now it will be flagged inconclusive.

Fix fill usage by passing Color.Transparent color

Fixed inproper use of UTF8Encoding. As it was written before, UTF8Encoding.Default actually returns base class static property Encoding.Default which is system's default ANSI code-page based encoding that is not UTF8.

Fix rendering error on 64 bit IIS, ColorBlend position must be betwee…