Patch: G1/G2 to the faces beside the loop, general and N-sided loops, points (#759) (#1521)

Thanks @jyviko.

crates/doc/src/format/pending/patch-continuity-and-points.rs

@@ -0,0 +1,6 @@
+//! A `Patch` on edges can carry `continuity` (`all`: `g0`, `g1` or `g2`, and `edges`:
+//! `[{edge: [x, y, z], g}]` for edges met otherwise; G0 everywhere when absent, and then not
+//! saved) and `points` it passes through (none when absent). Older designs need no
+//! transformation: a patch without them fills as it always did; a loop that is not a height field
+//! over its plane, which 0.13.0 refused, now fills with one face. 0.13.x asks for an update
+//! instead of dropping them.