add tests

[duckinator]

Tests for the following would be a really good starting point:

• Jim.load_spec(file)
• Jim::Client + Jim::Config
• Jim::TypedArray
• Jim::TypedHash
• Jim::Cli.run(['pack']) (equivalent to jim pack)
• Jim::Cli.run(['build']) (equivalent to jim build)
• Jim::Cli.run(['clean']) (equivalent to jim clean)