Float and String generators won't work in PHP 7

[MontealegreLuis]

Hi,

Float and String won't be valid class names in PHP 7.

http://php.net/manual/en/reserved.other-reserved-words.php

They could be renamed to something like FloatGenerator and StringGenerator. If you think those are good names I could create a PR for this.

[giorgiosironi]

Yes, these are good names.it's a diffused convention to use "{$qualifier}{$interface}" and $interface is Generator here.

[giorgiosironi]

Considering closed by #56