Optionally leave shorthand instead parsing values

Using shorthand notation in CSS is good practice so even if there are duplicates in most cases is better to leave them. 

Example test.css:

```
.foo { 
	border: 1px solid #000; 
	color: #000; 
	padding: 10px 5px; 
}
.bar { 
	border: 1px solid #fff; 
	color: #000; 
	padding: 10px 2px; 
}
```

If we run ```csscss -v test.css -n 1``` we'll get that there are 5 duplicates:

{.bar} AND {.foo} share 5 rules
  - border-style: solid
  - border-width: 1px
  - color: #000
  - padding-bottom: 10px
  - padding-top: 10px

However, in this case splitting border or padding shorthand notation is not good practice in CSS because file will be larger.
With <b>--use-shorthand</b> option shorthand will not be parsed so we'll get only one duplicate.

```csscss -v test.css -n 1 --use-shorthand```

{.bar} AND {.foo} share 1 rule
  - color: #000