Menu: act on a single keypress instead of waiting for Enter

Also stops Enter from quitting the menu (it used to share the quit branch with
q) and swallows the tail of an escape sequence, so one arrow key redraws once
rather than three times and never closes the menu.

Makefile

@@ -8,7 +8,7 @@
 # Overridable so a packager can pass the version it is actually building
 # (`make VERSION=$pkgver`). The literal below is the fallback for builds
 # straight from a checkout, and is what a release tag has to carry.
-VERSION      ?= 1.0.2
+VERSION      ?= 1.0.3
 
 PREFIX       ?= /usr
 DESTDIR      ?=