Max length settings are not enforced

[mattfletcher]

Sage Pay limits the length of most of the fields submitted. They are detailed here:

https://www.sagepay.co.uk/file/14206/download-document/FORM_Integration_and_Protocol_Guidelines_050115.pdf?token=jwimtbXQc-MmWWdGJHNJZFeshXg2re_chVFqiebQ2wc

As far as I can see, this library doesn't check for that. Failing to limit them will cause the POST to fail.