Remove broken printing_in_wx.py example.

It shows a preview, but writes blank files.  The wx printer
support has been deprecated for more than 2 years.
Merge pull request #1756 from efiring/del_wx_print_example

Remove broken printing_in_wx.py example.
Aternative to #1777.  Properly closes the paths returned by clip_to_rect and adds a new clip_to_bbox method to Path that returns a Path object.  Adds a test that tests clipping compound paths and multiple subsegments.
Use `np.empty` for a small speed improvement.
Document that clip_to_bbox requires closed paths.
Merge pull request #1778 from mdboom/clip_path_to_rect

Fix clip_path_to_rect, add convenience method on Path object for it
Fixed merge conflict on test_patches.