rounded_polygon() now copes with the degenrate case when tangents int…

…ersect to form a sharp corner with no arc.

Added an offset() function with some limitations.

Merge branch 'martinbudden-extrusion1515_dimensions'

Added convexity parameter to clip().

Fixed vero() constructor documentation.

Fixed missing space in veroboard vitamin decription.

Added usb_miniA().

Printed screw_knob() is now fully customisable by passing a parameter

list, constructed by screw_knob(), in place of the screw.

Screws can still be passed for backwards compaibility.

Documented insert_hole_length().

Merge branch 'MorrieG-master'

Added functions for generating twisted cable paths and calculating it…

…s radius.

Top row of cable bundles reversed to match a twisted cable.

Fixed ziptie bug for small wires and corners made sharper.