Update docs/wiki

[Ma27]

It occurred to me that some parts of the development pages in the Wiki are slightly outdated (which is at least partly my fault as I didn't write some documentation about cargo-workspaces and cargo-make yet).

I'd go through the wiki and readme pages in the repository during the next days to fix/improve the following aspects:

• More details about project structure (e.g. how to build?, how to create a new crate?, when to add further tasks?, how to update the rust channel for everybody?, etc.)
• Reread the Git proposal (it's actually way too long and could be shortened before a decision about incorporating the proposal can be taken)
• Update frontend docs (build with cargo-make, common pitfalls (e.g. conflicting stack pointers), probably sub-pages about the history of the shared-memory implementation)
• Basic documentation about tools and math helpers (at least basic descriptions and simple usage examples)