Add is_re() and is_reg_exp().
Add string functions:

- camel_case()
- capitalize()
- ends_with()
- escape_reg_exp()
- escape_re()
- kebab_case()
- pad()
- pad_left()
- pad_right()
- repeat()
- snake_case()
- trim()
- trim_left()
- trim_right()
- trunc()
Use "//" for division to ensure remainder is dropped in Python3.