Rename functions to more short names

- Rename function `lowercase` to `lower`;
- Rename function `capitalize` to `title`;
- Rename function `uppercase` to `upper`.
Implement bats tests
Convert separator to camel case

Create a function called `sep2cc` that converts a separator to camel
case string.
Convert camel case to a separator

Create a function called `cc2sep` that converts the camel cases to a
defined separator.