The original `key_reader` program was useful but didn't do much that `xxd`
or `od -tx1z` didn't do. Furthermore, it wasn't built and installed by
default. This change adds features that make it superior to those programs
for decoding interactive key presses and makes it a first-class citizen
like the `fish_indent` program that is always available.
Fixes#2991
Remove the "make iwyu" build target. Move the functionality into the
recently introduced lint.fish script. Fix a lot, but not all, of the
include-what-you-use errors. Specifically, it fixes all of the IWYU errors
on my OS X server but only removes some of them on my Ubuntu 14.04 server.
Fixes#2957
