[cleanup] Remove unused constants
[clang-cl] libs after LDFLAGS
diastddia.py: fill_ellipse did stroke, not fill
dox: mention Graph Layout plug-in
svg: respect "inherit" and some bezier robustness

Not setting the style when the value 'inherit' is given makes W3C's
struct-group-03-t.svg test case almost pass. It avoids a font-height
of 0 and preserves some color settings. Still unsupported are
currentColor and the display attribute.
Also some robustness against closed path with too few points.
svg: warn about a closed path with just two points

Dia's Beziergon wants at least three points, but some SVG only
have pathes with just two points. Turn these into a BezierLine
and throw a g_warning(), because I'm uncertain if these shouldn't
be handle differently.
[clang-cl] Avoid redefinition of isnan and is isinf
plugin: Use the Freetype developer's proposed way if #include'ing their headers.

Allows us to build against Freetype 2.5.1 (without breaking older
versions).

https://bugzilla.gnome.org/show_bug.cgi?id=720573

Signed-off-by: Hans Breuer <hans@breuer.org>
[diagram-as-object] Misc - NewGroup is gone, welcome Misc - Diagram
svg: support for external SVG in <image/>

Importing svg as "Misc - Diagram" should produce better results than
GdkPixbuf rendering of SVGs, especially when there is no librsvg
plug-in installed ;)
DiaContext w/o dia_context_set_filename is legal
[path] tweaking of rotate via handle

This is still not completely working as expected, e.g. no proper undo.
Maybe rotation should not be done via handle but via context menu or
properties instead?
[image] message_error message should have trailing \n
svg: support 'color' attribute and 'currentColor' value at import

It was just too easy to make the test suite test fail on it.
[gradient] introduce DiaPattern object

Step 1 of 7 for gradient support in Dia: the basic object currently can
hold radial and linear gradient information.
[gradient] add pattern standard property

Step 2 of 7 for gradient support in Dia: glue between pattern object
and diagram objects, including serialization support.
[gradient] interface definition DiaRenderer::set_pattern()

Step 3 of 7 for gradient support in Dia: renderer interface extension
to detect pattern capability and use it.
[gradient] Standard - *: use pattern property and perform fill with it

Step 4 of 7 for gradient support in Dia: the standard objects used for
most importers now have a pattern property.
[gradient] svg: import gradients and set them on objects

Step 5 of 7 for gradient support in Dia: parse gradient information from
SVG and set the pattern property for respective objects.
[gradient] cairo: implement DiaRenderer::set_pattern()

Step 6 of 7 for gradient support in Dia: render gradients with cairo.