make completion result more informative

Currently when looking at completion result, it's hard to understand, what is the type value of particular key:

```
[3] ngx(content)> ngx.loca        
ngx.localtime  ngx.location
```

where 
- `ngx.localtime` is a function
- `ngx.location` is a table

Make it more information so it will be easy to make a difference between:
- table
- function
- userdata
- cdata (?)
- the rest of lua types
