v0.1.3

A big idle-CPU cut: the run loop blocks on the windowing system's event descriptors instead of polling on a timer, so an idle Lantern app drops from about half a CPU core to a fraction of that (roughly 44% to 8% in a Slate desktop build), with no change to responsiveness. Requires sigil 0.17.18 for await-readable-fds. Existing projects build without changes.