Another step in moving these APIs toward the common object oriented and
declarative paradigms used by other APIs.
This commit introduces the `awful.keyboard` module. It currenly only
exists as a placeholder for the first few append/remove function, but
will grow in scope in another pull request to expose the currently
private modifier APIs and to provide keybindings collision detection
and replace some of `awful.hotkey_popup` business logic.
The `keygrabber` tests which uses root keybindings are disabled for
now to keep the commit size small. This is necessary since the shims
will need many iterations of changes before this work again with the
new syntax.
Locally I got this, where only two xterms were opened.
```
% tests/run.sh test-awesomerc.lua
awesome_log: /tmp/tmp.ToAKs6Gw4J/_awesome_test.log
== Running test-awesomerc.lua ==
Error: timeout waiting for signal in step 1/11 (@20).
===> ERROR running test-awesomerc.lua! <===
Error: timeout waiting for signal in step 1/11 (@20).
There were 1 errors!
```
