Fix #185: Multiline text is not rendered. Tspan is nested/child element to text element and it was not considered for path

Fixed problems when running in multiple threads. The use of a static matrix and the use of StringFormat.GenericTypographic seemed to cause problems when used in multi-threading. This is resolved by making the matrix non static and use a copy of the StringFormat.

Also created a new exception for memory overflows. When using multithreading to render a large amount of big images the bitmap creation can fail (due to memory allocation) throwing an error. This is now caught and a specific exception is thrown.

Extended the Marker start/mid/end getters with a function to return null if the property was set to none. This will prevent nullpointer issues when having none as one of the items.

Skip to consider Symbol element directly, because it is calculated through reference from use element

Fix #55 : Call Path in a SVG with an empty content element causes an InvalidArgumentException[updated]

Infinite loop in SvgRadialGradientServer CalcScale Issue #163

SvgDocument as Write(XmlTextWriter); allowed elements to decide whether or
not they should be written. E.g. text elements should not be written
unless they have children.

Fixed many attribute enums. Now they will 1) output the proper case, 2) only output if non-null and non-default, 3) include more documentation, 4) are marked as Flags where appropriate.

SvgDocument as Write(XmlTextWriter); allowed elements to decide whether or
not they should be written. E.g. text elements should not be written
unless they have children.

Fixed many attribute enums. Now they will 1) output the proper case, 2) only output if non-null and non-default, 3) include more documentation, 4) are marked as Flags where appropriate.

Stop crash on null or empty images
Deal with multiple spaces in Matrix

More serialization bug fixes and better fallback for font definition
problems.

Added parameter to the SvgAttribute indicating whether the storage is
the _attribute dictionary.  If true, the output will only be serialized
only if the key is in the dictionary.  This structure is an alternate to
the SvgDefinitionDefaults class.