Improve the way we print an individual transformer

[npatki]

Problem Description

Users who are inspecting a transformer want to know the hyperparameters that are being used to create it. To improve usability, we should improve the way each individual transformer is printed.

Expected behavior

Every individual transformer should print:

• name of the transformer
• hyperparameters used to create it (ie all hyperparameters that are not the default)

Goal: User should know exactly how to create that object.

# Default: No parameters are printed because they are all defaults
>>> from transformers.numerical import FloatFormatter
>>> default_transformer = FloatFormatter()
>>> print(default_transformer)
<FloatFormatter()>

# Overriding parameter(s): Only print the overridden parameter(s)
>>> from transformers.boolean import BinaryEncoder
>>> transformer = BinaryEncoder(missing_value_replacement='mode')
>>> print(transformer)
<BinaryEncoder(missing_value_replacement="mode")>

Additional context

One motivation for this change is the HyperTransformer. When it returns the (first) transformer for each column, it will be nice if users can see which transformers are being used.