Added round linejoin, but would be better with antialised polyfill
Risky: antialiased fill, linejoin fix, and png support

Note:

antialias fill is kind of cheating bc only draws an antialiased
simpleline along the coords, but does look okay...

linejoin was fixed to avoid empty holes where lines overlap, but only
temporary, not perfect, and for polygons first and last outline dont
become connected

images can now be saved in png format using pypng (though may need some
tweeking to make sure image transparency works...)
polyjoinfix, put/get fix, load png feature

Basically works now, except minor issues.

Also moved some functions to a geomhelper submodule