Data conversion

[0xWaleed]

Implementation of data conversion from upper case to lower case and vice versa using
bits manipulation and wrote tests for all possible cases.
Both functions takes const ref to avoid copying and construct a local string variable
then return it with implicit move semantic without changing the input.
I did all my best to comply with the guidelines.

I am open to any change requests on this PR and please detail the changes with reasons so I can learn. 🥰

Thanks.

• Read the contribution guidelines
• Added unit tests (or unit tests have already been added)
• Updated the Contents

Closes #99

[0xWaleed]

@faheel @alxmjo sorry for the mention, it took me some time to do this just for contribution and I would love to hear a feedback from you. I know you are busy and excuse me for this. 😊

[stale]

This issue has been automatically marked as inactive because it has not had recent activity. It will be closed in 15 days if no further activity occurs. Thank you for your contributions.

[0xWaleed]

@faheel Sorry is supposed to be discarded ?

[0xWaleed]

Not worth my time. should be archived if not maintained. Thanks @faheel , @alxmjo