Celsius to Fahrenheit Conversions (#2188)

* added conversions between celsius and fahrenheit

* Renamed celsius_to_fahrenheit.py

* Fixed spelling issues

* modified file to fit the 88-character limit

* added changes to pass the travis-ci test

* further changed the files to pass the travis-ci test

* further changed the files to pass the travis-ci test

* Shortened conversions/fahrenheit_to_celsius.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Type hints added to conversions/fahrenheit_to_celsius.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* changed the code to let the caller do the printing

* addressed the changes made on github

* Added Kelvin conversions and put temperature functions in a single file

* Removed whitespace from a blank line

* Update temperature_conversions.py

Co-authored-by: Christian Clauss <cclauss@me.com>