Additional module kinds and modifications to existing kinds

[GraphR00t]

Library (new)

• Limited internal state
  • The values of global variables cannot be mutated after the module have returned.
• Cannot define databases
• Importing a library always returns the same instance (?)

Service (new)

• Internal state
• Can define databases
• Importing a service always returns the same instance
• May be running in a different process or machine

Unspecified

• Should not be able to define databases
• Embedded child modules should be stopped when the module returns (?)

Spec

• Should not be able to define databases (manifest)

External dependencies (URL and package? imports) should expose themselves as librairies/services (?)