Fixed the tests and cleaned up some warnings

* The tests in `memstream.rs` were broken after the latest update. I fixed them.
* The camel case functions in codegen were changed to snake case. It souldn't affect the API.
* `phase(syntax)` is now written as `phase(plugin)`.
* `#![macro_escape]` shouldn't be necessary, so I removed it.

There is still the `MediaType` function. It's public, so it's in the API. Remove, rename or ignore?