Reproducible class with environment and code

Reproducible class with environment and code.

Slots

code: (character) representing code necessary to reproduce the environment
env: (environment) environment which content was generated by the evaluation of the code slot.
id: (integer) random identifier of the code element to make sure uniqueness when joining.
warnings: (character) the warnings output when evaluating the code
messages: (character) the messages output when evaluating the code