faker-generator

Hi,
Could you add a sentence generator?When generating some articles ,title and content are needed,content can be generated by randomdata.Paragraph(),but I don't find which one should be used for generating title.

For example:

// Print a sentence
fmt.Println(randomdata.Sentence())

There is a missing functionality in payment.rs.

• Add credit_card_luhn_number body, whould generate a proper luhn validated credit card number.

By default, the TestFiller uses a different seed for each instance. Depending on the usage a possible flaky test could be not desired. Currently, it would be required to add a fixed seed directly, but a special Class with a fixed seed by default could come handy.