Standardize module names - Transformation

[Abinaya Mahendiran]

The module number-to-word should be changed to number_to_word.

Solution:

• Rename the folder from number-to-word to number_to_word
• Add an entry number_to_word in the test/mapper.py file in the appropriate dictionary (either heavy or light transformation depending on the flag heavy)
• Once added, test the module by executing

pytest -s --t=number_to_word