Add support for multiple key strokes combinations

[mrmarktyy]

Add support for multiple key strokes combinations, for example,

key('ctrl+r+s', function(){ alert('stopped reload!'); });
key('ctrl+shift+r', function(){ alert('reload!'); });
key('command+alt+p', function(){ alert('pause!!'); });
key('command+shift+w+p', function(){ alert('do something!!'); });

[mrmarktyy]

Hi, Please let me know if you have any suggestion before merging in. Thank you