check for json_last_error() - fix eversign#13

fix result of cancel/delete document

renamed isCanceled to isCancelled to be consistent with the API

autogenerate signing order and add some flags to create document

fix guzzle and jms to minimum not exact version

add language parameter to Signer and Recipient

add some new fields + improve example

- embedded_signing_enabled
- flexible_signing
- use_hidden_tags
- expires

add sandbox parameter

change all booleans to integer internally

switch debug mode to false