Add `Record` print methods

[lazappi]

Adds to_string() and print() methods to the Record class and a (incomplete) describe() method to the Artifact class.

Fixes #5, replaces #3

[lazappi]

The output is similar to Python with the following differences:

• Order is fixed but not always the same, it's defined in the method
• The id and created_at fields are printed
• Colour (this can be turned off)

There is also an incomplete describe() method. It only shows the provenance fields in the example at the moment. Labels, features, other provenance etc. should be possible but I need to work out how to properly locate things which will take more work.

Examples

Artifact

Python

R

R (style = FALSE)

Storage

Python

R

Describe Artifact

Python

R