Improve developer documentation

The documentation is okay for users, but the developer documentation is very slim. This ticket is to add additional explanations of how the code works, how to debug the system, and provide enough information that someone could write some standalone tools to use a signet if they were so inclined.

Note: This change (branch: 40-improve-developer-documentation) should be merged in after the changes for #37 (closed) (branch: 37-screen-reader-compatibility).