Add breaklines to high level mesh interface

[ole]

Augment create_mesh_from_regions to include keyword argument:

breaklines=<list of polylines>

Issues:

• Does polyline have to connect to other lines
• What if polyline is tiny
• What happens if polyline goes outside bounding polygon?

[ole]

Will the low level interface "add_points_and_segments" do it? If so, update the manual to explain better.

[ole]

By the way - the poly's should not be closed and this code should check for this and possibly remove one duplicate end points.

[James Hudson]

New interface has been added. create_mesh_from_regions can take a list of breakline polygons, like so:

create_mesh_from_regions(..., breaklines = [east+1000,north+2000], [west,south?, read_polygon('shallow.csv')]))