misc bugfixes
bugfix voronoi's dual: yield in the loop to test all edges candidates
add epsilon to collinearity test, plus a demo
clean triangulation subfunctions

Get ride of the logical operator and use cleaner bounding notation.
Add exclude_edges to is_acute.
bugfix filter acute triangles
add a theme system and a theme with more beautiful colors
save images with the depth in the filename

same dpi for both png and svg
First implementation of indexed quad trees
Quadtrees based on hashed datastructures rather than indexed ones
Add queries to quadtree.

Cleaner quadtree code and comments