NE-ON: multiline string support

I tried to make a pull-request, but got lost in the `Tokenizer` insides.

I propose using the python multiline string syntax.

From NE-ON:

``` python
"""
this
is
"multiline"
'string'
"""
```

To PHP:

``` php
"this\nis\n\"multiline\"\n'string'"
```
