Fix escapejs return type

[tomekowal]

This commit changes escapejs filter to return binary, when it received binary as input.

Couple of weeks ago I proposed to use unicode:characters_to_list in escapejs to fix a bug
with handling 'line separator' and 'paragraph separator'.

Even, when it got binary as input, escapejs returned list as output,
so I left it that way, but I believe, it should return binary, when it receives binary.
For example first filter works this way.

[kaos]

You are right. I think there's been a policy of binary in should yield binary out.

I would like the actual escape routine to be implemented using binaries, though, to avoid the doubly converts when using binaries (as I prefer binaries over lists), or if needs must, to have a dual implementation. But that is not the issue here.