nl2br - fix inline string

From Twig/test/Twig/Tests/Fixtures/filters/nl2br.test:
{{ "I like Twig.\nYou will like it too.\n\nEverybody like it!"|nl2br }}

Should have become:
You will like it too.<br />
<br />
Everybody like it!

But was:
I like Twig.\nYou will like it too.\n\nEverybody like it!

This is because newlines were escaped in string literals like that, this
patch handle those as well
Twig filter twig is suppose to escape HTML and should take a character_mask list

This isn't actually documented in their API docs but was in their
tests:
trim is suppose to escape HTML.

twig.js didn't implemenet: the character_mask argument.

This commit fixes both
Merge pull request #79 from m-abs/master

Newline in string literals weren't handled properly.