Fixed up pipe character support in split

[amit777]

Hi, we found a bug when trying to split on a | character

use Template::Liquid;

my $template = Template::Liquid->parse('{% assign fragments = foo | split: "| |" %}{% for fragment in fragments %}frag={{fragment}} {% endfor %}');

print $template->render(foo => "foo| |bar| |baz")

This patch will do negative lookaheads and look behinds to make sure a pipe is not surrounded by quotation marks. It will also quotemeta the split character sequence.

[amit777]

related to ticket #24