[FEATURE]: Start implementation of native dxf export
Write dxf header and eof
First implementation of dxf feature writing (but it does not work yet)
Write additional header field and table section
Dxf: add more header fields, min/max extent and a test linestyle
More symbology updates for dxf
Prepare color palette matching for dxf
Feature #8725: Fast rendering of geom (v-OGR)

Implements fast rendering of LineStrings and Polygons pre-applying a
view threshold filter to the geometries to render in qgis. Also disable
'Antialiasing' when it is possible.

View Table of test results in 'http://hub.qgis.org/issues/8725'

(This version of branch implements the improvement in vector-providers)
Feature #8725: FastRendering of geometries

Implements fast rendering of LineStrings and Polygons pre-applying a
view threshold filter to the geometries to render in qgis. Also disable
'Antialiasing' when it is possible.

View Table of test results in 'http://hub.qgis.org/issues/8725'
Feature #8725: Fast rendering of geometries

Fix compile errors: include "std::limits"
Feature #8725: simplification configurable

The simplification is configurable by layer, also this commit contains
reording of code.

I have pending show in the properties form of layer a check for
enable/disable the simplification
Feature #8725: check QgsFeatureRequest::NoGeometry
Feature #8725: Fix dpi bug
Feature #8725: Minor improvement
Feature #8725: Remove unnecesary setPen()
Feature  #8725: Show configuration option

Shows a new rendering tab in the layer options form for configure the
drawing simplification.
Feature #8725: Increment 2x the factor in slider
Feature #8725: drawConvexPolygon() can be faster

On some platforms (e.g. X11), the drawConvexPolygon() function can be
faster than the drawPolygon() function.

https://qt-project.org/doc/qt-4.8/qpainter.html#drawConvexPolygon
Feature #8725: Replace '*foo=bar' by 'memcpy'
Feature #8725: Disable simplify in editmode

Disable the drawing simplification when the editmode is enabled, the
geometries are cached for snapping