Add available states constants
Add available states constants

| Q             | A
| ------------- | ---
| Branch        | master
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | proprietary
| Doc PR        | no

Facturama/facturama-php-sdk