Moved textcraft.py for testing purposes + functions' details fixed

[cxgonzalez]

What

• Created src/textcraft folder. Inside, i moved the textcraft.py file and created the init.py file to be able to import the functions to the test_textcraft.py file
• Modified functions (mostly using the same to_lowercase function) for snake_case and kebab_case
• Modified camelCase logic to be able to choose UpperCamelCase or lowerCamelCase. Defaults to lowerCamelCase
• Fixed the definition on a special snake case... case.

Why

• This new structure allows to correctly import the functions from src folder to the test folder and initialize those, so changes there can immediatly be tested and validated. Might require the "pip install -e ." command to import the local library in editable mode.

Notes

• I understand that everyone uses or prefers this or that structure, so if its not to the author's liking, feel free to ignore that part as long as it works for you during development!
• While the structure change is "optional", i do believe its worth to see the changes to the functions in textcraft.py, so they can match the desired outputs on the test file.

[O-sama12]

LGTM, but takes some times to get merged, feel free to look up for other issues.