Add code templates

I added some code template.

### How to use
1. expand with `Tab` key   
e.g. type `link` then `Tab` -> `[name](http://)` : first, stop at `name`, if we type something and press enter key, target text is moved `http://`.

2. code completion : i.e. `Ctrl` + `Space` (perhaps, NB74)  
e.g. type `l` then `Ctrl` + `Space` : we can see some candidate items on code completion list. (link, linkt, ....)

3. surround text : `Alt` + `Enter`  
select text then `Alt` + `Enter` : we can surround text with `*`, `**` and ``\``

Thanks.