new: graphics/py-pygal

Hi,

Here a new python port: graphics/py-pygal

http://pygal.org/en/stable/

It is an optional dependency for a tryton module (sale).

pygal is a python svg graph plotting library.

it provides various kinds of charts:
- Line
- Bar
- Histogram
- XY
- Pie
- Radar
- Box
- Dot
- Funnel
- SolidGauge
- Gauge
- Pyramid
- Treemap
- Maps

I was not able to enable the test suite on the port. It requires several
dependencies not packaged.

Another thing surprised me: it seems that devel/py-test-runner is
required to build. I dunno if it is usual or not.

Any comments or OK ?

Thanks.
--
Sebastien Marie