{{}} will crash

[epage]

From @bananenmannfrau cobalt-org/cobalt.rs#307

The following post will crash the application when building/watching

extends: default.liquid

title: test 
date: 14 January 2016 21:00:30 -0500
---

test {{}}

The {{}} are the problem. Also when enclosed in ``

The output of RUST_BACKTRACE=1 cobalt watch is:

[info]   Using config file .cobalt.yml
[warn]   Syntax theme named 'base16-ocean.dark' ignored. Reason: Themes are unsupported in this build.
[info]   Building from . into build
thread 'main' panicked at 'index out of bounds: the len is 0 but the index is 0', $HOME/.cargo/registry/src/github.com-1ecc6299db9ec823/liquid-0.10.1/src/parser.rs:43:11
stack backtrace:
   0: std::sys::imp::backtrace::tracing::imp::unwind_backtrace
   1: std::sys_common::backtrace::_print
   2: std::panicking::default_hook::{{closure}}
   3: std::panicking::default_hook
   4: std::panicking::rust_panic_with_hook
   5: std::panicking::begin_panic
   6: std::panicking::begin_panic_fmt
   7: rust_begin_unwind
   8: core::panicking::panic_fmt
   9: core::panicking::panic_bounds_check
  10: liquid::parser::parse
  11: liquid::parse
  12: cobalt::document::Document::render_html
  13: cobalt::cobalt::build
  14: cobalt::build::build
  15: cobalt::serve::watch_command
  16: cobalt::run
  17: cobalt::main
  18: __rust_maybe_catch_panic
  19: std::rt::lang_start