key-kill-mode: a page-mode for blocking keyup and keydown events

Key-kill mode is a generic page-mode that can be used on any site for
blocking keyup and keydown events.  To use it, load the module and add
tests, like this:

    require("key-kill");
    key_kill_mode.test.push(build_url_regexp($domain = "github"));
    key_kill_mode.test.push(/\/\/.*slashdot\.org\//);