Support "none" in Fill value if inherited from parent

If elements are nested in groups and have different fill values than
their containing group the fill value wouldn't be written correctly.

Embedded transformations were not being applied correctly; they were
being done in reverse order.

- Changes to get texts displaying bold / normal weight
- Changes to get textspans work correctly
- Made (semi-hardcoded) document metadata section - allow reading and regurgitating metdata tag from an original source document
- Included image
- Modified paths to allow for scientific notation
- Included ability to have markers for path ends (arrow ends etc)

* fixed missing files

* added implicit operator from RectangleF to SvgViewBox

* SvgDocument can calculate its size in percentage
* SvgTransform collection can return all matrices multiplied

* added method to collect paths of children elements
* fixed possible bug getinheritedattribute

* fill can be null -> none in XML
* added type converters for enums
* added type converter for unitcollection
* fixes several viewbox bugs
* document can now draw into a given bitmap
* content of SVG tag is written (used by the text tag)
* changed font handling in text element, still need proper alignment
* changed intersparse character of SvgTransformConverter.cs to space, because inkscape couldn't parse comma
* added class diagram for basic shapes

- Adding initial support for Write functionality. Units & Transforms mostly. Enums still need work. Needs support for an IsDirty concept so that that every possible attribute isn't written.

- Refactored SvgElementFactory to use the new SvgElementAttribute to get available elements.

- Fixed #6324: SvgElement.PushTransforms and ViewBox - not necessarily related to ViewBox but every   element was 'resetting' the current graphics transform if the element contained it's own transform. This 
  was a very small fix for a large problem (SvgElement.PushTransforms Matrix transformMatrix = new   Matrix(); changed to Matrix transformMatrix = renderer.Transform; in order to inherit the current   transform.)
- Fixed #6344: Parsing document incorrectly parents elements when it encounters empty nodes which are   in a different namespace. Empty nodes are now ignored and current nodes are closed as required. We'll 
  see how this fix goes.
- Fixed #6381: Units in inches are incorrectly parsed as millimeters - problem was caused by some   copy/paste work.
- Graphics has been replaced by SvgRenderer. This is essentially a wrapper around graphics but will allow
  custom svg related properties in the future when needed.
- Removed ISvgRenderer: A concrete implementation is suitable.
- SvgElement.ElementName has been changed to non-virtual and is set by the parser instead of the   developer having to specify it when developing the class.
- Added more XML API documentation.

- Fixed support for text-anchor="middle" and text-anchor="end" for <text/> elements.
- Added more XML API documentation
- Added x attribute and y attribute support to <use/> elements.