liquid 0.13.4

The liquid templating language for Rust
Documentation
Thanks for wanting to contribute! :snowman:

Feel free to create issues or make pull requests, we'll try to quickly review them.

If you need assistance, you can join the `#cobalt` channel on `irc.mozilla.org` or the Gitter chat [![Gitter](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/cobalt-org/cobalt.rs)

We want you to feel safe and welcome and will enforce the **[The Rust Code of Conduct](https://www.rust-lang.org/conduct.html)** on all communication platforms of this project.
Please contact [@johannhof](https://github.com/johannhof) for questions or in cases of violation.

# Issues

This project aims to be a Rust implementation of [Liquid](https://shopify.github.io/liquid/).
- Notice that we deviate from shopify/liquid? Please, open an issue if there isn't an [existing one]https://github.com/cobalt-org/liquid-rust/labels/shopify-compatibility
- Want a new tag or filter? Check for an [existing issue]https://github.com/cobalt-org/liquid-rust/labels/enhancement and open one if needed.

Some helpful pieces of information when reporting issues
* liquid-rust version
* rust version
* OS and version

# Pull Requests

## Project Ideas

If you're looking for things to do check out the [open issues](https://github.com/cobalt-org/cobalt.rs/issues), especially those with the
[easy](https://github.com/cobalt-org/liquid-rust/issues?q=is%3Aissue+is%3Aopen+label%3Aeasy) and [help wanted](https://github.com/cobalt-org/liquid-rust/issues?q=is%3Aissue+is%3Aopen+label%3A%22help+wanted%22) flags.
Or take a grep through [all TODO comments](https://github.com/cobalt-org/liquid-rust/search?q=TODO) in the code and feel free to help us out there!

## Best Practices

We appreciate your help as-is.  We'd love to help you through the process for contributing.  We have some suggestions to help make things go more smoothly.

🌈 **Here's a checklist for the perfect pull request:**
- [ ] Make sure existing tests still work by running `cargo test` locally.
- [ ] Add new tests for any new feature or regression tests for bugfixes.
- [ ] Install [Clippy]https://github.com/Manishearth/rust-clippy and run `rustup run nightly cargo clippy` to catch common mistakes (will be checked by Travis)
- [ ] Install [Rustfmt]https://github.com/rust-lang-nursery/rustfmt and run `cargo fmt` to format your code (will also be checked by Travis)

For new tags or filters, we recommend
- Open an RFC Issue for discussing what the API should be.  We'd like to avoid disrupting people once they start using a feature.
- Consider incubating it in your code first to so it can be iterated on to find what works well.
- Checkout prior art with [Shopify's proprietary extensions]https://help.shopify.com/themes/liquid or [Jekyll's extensions]https://jekyllrb.com/docs/templates/.
- Putting all non-standard features behind feature flags.

If you're interested in benchmarking your changes
- Be sure to get some before and afters on the same machine
- Rust nightly is required.  You'll need to run `rustup run nightly -- cargo bench`

Hopefully we get this integrated into your CI process.

# Releasing

When we're ready to release, a project owner should do the following
- Determine what the next version is, according to semver
- Bump version in a commit
  - Run `clog --setversion <X>.<Y>.<Z>`, touch up the log
  - Update the version in `Cargo.toml`
- Tag the commit via `git tag -a v<X>.<Y>.<Z>`
- `git push upstream master --tag v<X>.<Y>.<Z>`
- Run `cargo publish` (run `cargo login` first if needed)
- Update README.md to list the new version for Cargo.toml