Extract line numbers from HTML

Closes #5 

- [x] Extract line numbers from translate directive
- [x] Extract line number from translate filter

The line number extracted will be the line number of the opening tag that hosts the translate directive. For example, the line number for `Foo` in the following example would be 1, even though the translate directive is on line 2 and the text begins on line 3. 
```html
<div
  translate>
    Foo
</div>
```

The same holds for uses of the translate filter with no delimiters. For example, this will extract the line number 1 for `Bar`:
```html
    <div
            foo="'Bar' | translate"></div>        
```

However, when you use the translate filter with delimiters, the actual line number of the filer will be used. For example, the following will extract line number 2:
```html
<div
   foo={{'bar' | translate}}></div>
```