Apart from turning off Auto Layout for the Demo project, the only
thing remaining was several __weak qualifiers to prevent retain
cycles in blocks. I have replaced them with __unsafe_unretained
since __weak is not supported on 10.6. There should be no safety
concerns here, since we are certain the pointers will remain valid.

Mostly back to the previous version with enable/disable checkboxes &
one settable and one hard-coded shortcut. I have tried to come up with
a nicer pattern to watch the enabled/disabled checkboxes, but without
external dependencies like Facebook’s KVOController I didn’t come up
with anything better than plain old KVO.

This returns the associatedUserDefaultsKey property used in previous code
versions, only the implementation uses less magic.

I have replaced the modal alert with a beep, it’s faster to test
without having to close the alert.

This adds a really simple API to set up some bindings without having
to keep a binder instance around by hand. If somebody wants to, it’s
not a problem to allocate a separate instance and have precise control
over its lifetime.

There can only be one Carbon event handler, so it doesn’t make sense
to create multiple instances of the shortcut monitor.

This is a big change that was hard to split into smaller commits. There’s now
a new class to bind shortcuts to actions, a new class to bind user defaults’
keys to actions, and a new way to associate user defaults with the recorder
control (MASShortcutView). I have also updated the demo app to go with the
changes.

The new class to associate shortcuts with actions is called MASShortcutMonitor.
It wraps the Carbon hotkey magic and offers a simple interface to add a
shortcut along with a block that should be run when the shortcut is pressed.
It’s the lowest-level interface.

Since the usual requirement is to store the shortcuts into user defaults,
there’s also a higher-level interface offered by the MASShortcutBinder class.
That takes a defaults key and associates it with a block. When the shortcut
stored under the defaults key changes, the binder automatically switches to the
new shortcut. The class is a wrapper built atop of the previous one, the
MASShortcutMonitor – it simply adds, updates and removes shortcuts as the
user defaults change.

I have removed the special user defaults integration code from the recorder
control (MASShortcutView) and replaced it with a small Cocoa Bindings shim.
This means that in order to keep the recorder control in sync with the defaults
you just have to call the usual bind:toObject:withKeyPath:options: method,
like this:

[_shortcutView bind:MASShortcutBinding
    toObject:[NSUserDefaultsController sharedUserDefaultsController]
    withKeyPath[@"values.ExampleDefaultsKey"
    options:@{NSValueTransformerNameBindingOption:NSKeyedUnarchiveFromDataTransformerName}];

That’s more verbose than the previous solution, but it’s much cleaner and can
be swept under a convenience call if needed. I might also add a dictionaryValue
property later that would make it possible to bind the value to user defaults
directly, without a transformer, and would enable backward compatibility with
Shortcut Recorder.

Now you can just `#import <MASShortcut/Shortcut.h>`.