Add method to update self-invoice settings

allow sending query parameters to create and edit customer (#36)

Merge pull request #35 from FacturAPI/hotfix/conditional_body_put

fix(conditionalPut): add ternary in $body for encode json or send null

Merge pull request #34 from FacturAPI/chore/validate_signature

chore(webhook): add validateSignature method in webhook flow

Merge pull request #32 from FacturAPI/fix/post_with_body_null

fix(execute_post): accept and validate nullish body in execute post m…

feat(exception): throw error object in unsuccesful responses (#30)

- Corrected method names: `update_draft` and `copy_to_draft`

- Added invoice methods: `update_status`, `edit_draft`, `stamp_draft`…

… and `copy`

feat(cancellation): add cancellation receipt pdf in library (#22)

Co-authored-by: Javier Rosas <javier.rosasb@gmail.com>

- Add method to download cancellation receipt PDF

- Improve error handling (thanks to @ingfdoaguirre)
- Fix email send bug