Bug#954144: key-mon: Relatively high CPU use on idle machine

[Lawrence D'Oliveiro]

Turns out there has been a little bit of further development on this
project since it was last packaged for Debian. I have imported the
original commit history from Google Code and rebased my changes on it.
My repo is available from GitHub <https://github.com/ldo/key-mon> and
GitLab <https://gitlab.com/ldo/key-mon/>. I have reduced the polling
frequency to 100 times a second. That still sounds high, but when I
dropped it to 10 times a second, it kept missing events.