added cache support, alias know to ask

now we can use ask or know (be more semantic)
```
var mayi = require('mayi');
mayi.ask('video', function(result) {
    // result goes here
});

or

mayi.know('video', function(result) {
    // result goes here
});

Change-Id: Iefb57e0e0e555a7c83e183b07eb156fb03faacf4