Add "encryptColumn" decorator

[chrisdickinson]

Similar to the autoNow, but it would take a column & a secret. Any reads from that column would automatically be encrypted with the secret on write and decrypted with the secret on read.

(Thanks for the feature request @whithang!)

[whithang]

actually the idea was to pass in a function and that function would be called on that column anytime the column exists in the input. then you can define exactly what you want to happen

[chrisdickinson]

WIP PR here: #105

This adds a prepJSData method on Columns, which is the first step towards implementing this functionality. The end-user facing API for it isn't set in stone yet – it might be that users pass orm.encrypted() much like they pass orm.fk() today. I could also see a use for a decorator, in that you could have two different views on the same data – one might automatically encrypt and decrypt, while the other only deals with the encrypted data.