REST enhancement #1: Allow one to get parameters from headers

Those changes set the basics block for handling origin of parameters.

The most basic one, `@fromHeader`, is already implemented, and the others are left undocumented so far.

Specifying the origin of parameter is important for interop with other framework (with a focus put on [Java Jersey](https://jersey.java.net/documentation/latest/index.html)), and for auto-generating various REST properties (e.g., auto implementing OPTIONS requires `@fromHeader`).

Pinging @Dicebot , as he helped with the design.