This is a (minor) breaking change. If `rocket.launch()` is the last expression
in a function, the return type will change from `()` to `LaunchError`. A simple
workaround that preserves the previous functionality is to simply add a
semicolon after `launch()`: `rocket.launch();`.
resolves#34
* All From* trait methods are now named like the trait.
* All From* traits have an associated Error type.
* Document all of the `form` module.
* Add codegen tests for auto-derived forms.
* The param parsing traits now live under Request.