Helical 1.2.0

Additions

• Tapping screw threads to ISO 1478, in all fourteen sizes from ST1.5 to ST9.5, via ScrewThread.tapping(_:) or constants like ScrewThread.st3p5.
• Cross recessed tapping screws: Bolt.phillipsCountersunkTapping(_:end:length:) for DIN 7982 and Bolt.phillipsPanHeadTapping(_:end:length:) for DIN 7981, in sizes ST2.2 to ST6.3. Each takes either a type C cone end or a type F flat end.
• TappingHole, a pilot hole for a tapping screw to form its own thread in, sized to the thread's minor diameter. Bolt.tappingHole(depth:) makes one to suit a particular screw.
• ConeEndBoltPoint, a screw end tapering to a point, for building custom fasteners. Available as BoltPoint.coneEnd(tipDiameter:).

Fixes

• Countersink now reads its angle as the included angle it documents; any other value previously produced its supplement, so a 50° countersink came out at 130°. The built-in screw standards all use 90° and are unaffected, but code passing any other angle should drop whatever it did to compensate.
• Bolt.hexSocketCountersunk now uses the nominal head diameter rather than the smallest in the tolerance range, making heads and their recesses up to 1 mm wider. Recesses from earlier versions seat only the smallest heads flush.