Svg group renderer [WIP]

[artemp]

See https://github.com/mapnik/mapnik/issues/4363 for details

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 85.81236% with 62 lines in your changes are missing coverage. Please review.

Project coverage is 74.16%. Comparing base (34c95df) to head (6350e1b).

:exclamation: Current head 6350e1b differs from pull request most recent head 62c449e. Consider uploading reports for the commit 62c449e to get more accurate results

Files	Patch %	Lines
include/mapnik/svg/svg_renderer_agg.hpp	82.98%	33 Missing :warning:
src/svg/svg_parser.cpp	50.00%	10 Missing :warning:
src/projection.cpp	0.00%	9 Missing :warning:
src/cairo/cairo_render_vector.cpp	86.66%	8 Missing :warning:
src/gradient.cpp	0.00%	2 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4364      +/-   ##
==========================================
+ Coverage   74.14%   74.16%   +0.02%     
==========================================
  Files         493      494       +1     
  Lines       31868    32003     +135     
==========================================
+ Hits        23628    23736     +108     
- Misses       8240     8267      +27     

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[mathisloge]

@artemp I think you will need to rebase from master so that the windows-ci will work again