Utils for the Fledger system

Some common utils used by the Fledger system. The most important is the Broker structure that is used throughout the code to link the different parts together.

Broker

I wanted to create a common code for both the libc- and wasm-implementation for Fledger. Unfortunately it is difficult by the fact that libc allows to use threads (and sometimes needs them), so some structures need to have the Send and Sync traits. But these traits are not available for all necessary websys-modules! So I came up with the idea of linking all modules using a Broker system.

In short, all input and output for a module are defined as messages. Then each module handles incoming messages and produces outgoing messages. Modules can be linked together by defining Translators that take messages from one module and translate them into messages for the other module.