Sugested module layout

lib.rs        // Entry points and initialisation
core.rs       // Handles all multi-threading and stuff

vault/
  mod.rs      // core code
  fs.rs       // All filesystem utilities
  
record/
  mod.rs      // core code
  version.rs  // versioning utilities

crypto/
  mod.rs      // core code
  encoding.rs // encoding utility functions

api/
  mod.rs       // ...
  rest.rs      // A RESTful API
  binding.rs   // Exports some C headers